jQuery Grid Plugin - jqGrid

I have the grid setup and working.  I run the export like this:

var jsonEx = JQ('#mygrid').jqGridExport({ 'exptype': 'jsonstring' });

This works fine the first time and I get valid json.  However, if I run the export function again, I get a json string that isn't valid.  FireFox gives me this error message:

Error: missing ] after element list
Source Code:
    [native code]

Here is the json string from the two export operations (sorry, this is a lot to paste):

#1 (valid json)
{"grid":{ "url":"http://localhost/test.php?action=get_grid_data", "height":500, "page":1, "rowNum":25, "records":30861, "pager":[{}], "pgbuttons":true, "pginput":true, "colModel":[{ "name":"cat_title", "index":"cat_title", "label":"Asset Type", "width":150, "hidden":false, "resizable":true, "sortable":true }], "rowList":[ 25, 50, 75, 100, 200 ], "colNames":["Asset Type"], "sortorder":"asc", "sortname":"id", "datatype":"json", "mtype":"GET", "altRows":false, "selarrrow":[], "savedRow":[], "shrinkToFit":false, "xmlReader":{ "root":"rows", "row":"row", "page":"rows>page", "total":"rows>total", "records":"rows>records", "repeatitems":true, "cell":"cell", "id":"[id]", "userdata":"userdata", "subgrid":{ "root":"rows", "row":"row", "repeatitems":true, "cell":"cell" } }, "jsonReader":{ "root":"rows", "page":"page", "total":"total", "records":"records", "repeatitems":true, "cell":"cell", "id":"id", "userdata":"userdata", "subgrid":{ "root":"rows", "repeatitems":true, "cell":"cell" } }, "subGrid":false, "subGridModel":[], "reccount":25, "lastpage":1235, "lastsort":0, "selrow":null, "beforeSelectRow":null, "onSelectRow":null, "onSortCol":null, "ondblClickRow":null, "onRightClickRow":null, "onPaging":null, "onSelectAll":null, "loadComplete":null, "gridComplete":null, "loadError":null, "loadBeforeSend":null, "afterInsertRow":null, "beforeRequest":null, "onHeaderClick":null, "viewrecords":true, "loadonce":false, "multiselect":false, "multikey":false, "editurl":null, "search":false, "caption":"Asset Items", "hidegrid":false, "hiddengrid":false, "postData":{ "_search":false, "nd":1265001160993, "rows":25, "page":1, "sidx":"id", "sord":"asc" }, "userData":{}, "treeGrid":false, "treeGridModel":"nested", "treeReader":{}, "treeANode":-1, "ExpandColumn":null, "tree_root_level":0, "prmNames":{ "page":"page", "rows":"rows", "sort":"sidx", "order":"sord", "search":"_search", "nd":"nd" }, "forceFit":false, "gridstate":"visible", "cellEdit":false, "cellsubmit":"remote", "nv":0, "loadui":"enable", "toolbar":[ false, "" ], "scroll":false, "multiboxonly":false, "deselectAfterSort":true, "scrollrows":false, "autowidth":false, "scrollOffset":18, "cellLayout":5, "subGridWidth":20, "multiselectWidth":20, "gridview":false, "rownumWidth":25, "rownumbers":false, "pagerpos":"center", "recordpos":"right", "footerrow":false, "userDataOnFooter":false, "hoverrows":true, "altclass":"ui-priority-secondary", "viewsortcols":[ false, "vertical", true ], "resizeclass":"", "autoencode":false, "remapColumns":[], "ajaxGridOptions":{}, "direction":"ltr", "recordtext":"View {0} - {1} of {2}", "emptyrecords":"No records to view", "loadtext":"Loading...", "pgtext":"Page {0} of {1}", "toppager":true, "width":1234, "sortable":true, "id":"previewGrid", "keyIndex":false, "tblwidth":150, "disableClick":false, "_height":64, "_nvtd":[ 486, 20 ], "totaltime":26 }}

#2 (invalid json)
{"grid":{ "url":"http://localhost/test.php?action=get_grid_data", "height":500, "page":1, "rowNum":25, "records":30861, "pager":[{"addEventListener":function addEventListener() { [native code] }}], "pgbuttons":true, "pginput":true, "colModel":[{ "name":"cat_title", "index":"cat_title", "label":"Asset Type", "width":150, "hidden":false, "resizable":true, "sortable":true }], "rowList":[ 25, 50, 75, 100, 200 ], "colNames":["Asset Type"], "sortorder":"asc", "sortname":"id", "datatype":"json", "mtype":"GET", "altRows":false, "selarrrow":[], "savedRow":[], "shrinkToFit":false, "xmlReader":{ "root":"rows", "row":"row", "page":"rows>page", "total":"rows>total", "records":"rows>records", "repeatitems":true, "cell":"cell", "id":"[id]", "userdata":"userdata", "subgrid":{ "root":"rows", "row":"row", "repeatitems":true, "cell":"cell" } }, "jsonReader":{ "root":"rows", "page":"page", "total":"total", "records":"records", "repeatitems":true, "cell":"cell", "id":"id", "userdata":"userdata", "subgrid":{ "root":"rows", "repeatitems":true, "cell":"cell" } }, "subGrid":false, "subGridModel":[], "reccount":25, "lastpage":1235, "lastsort":0, "selrow":null, "beforeSelectRow":null, "onSelectRow":null, "onSortCol":null, "ondblClickRow":null, "onRightClickRow":null, "onPaging":null, "onSelectAll":null, "loadComplete":null, "gridComplete":null, "loadError":null, "loadBeforeSend":null, "afterInsertRow":null, "beforeRequest":null, "onHeaderClick":null, "viewrecords":true, "loadonce":false, "multiselect":false, "multikey":false, "editurl":null, "search":false, "caption":"Asset Items", "hidegrid":false, "hiddengrid":false, "postData":{ "_search":false, "nd":1265001160993, "rows":25, "page":1, "sidx":"id", "sord":"asc" }, "userData":{}, "treeGrid":false, "treeGridModel":"nested", "treeReader":{}, "treeANode":-1, "ExpandColumn":null, "tree_root_level":0, "prmNames":{ "page":"page", "rows":"rows", "sort":"sidx", "order":"sord", "search":"_search", "nd":"nd" }, "forceFit":false, "gridstate":"visible", "cellEdit":false, "cellsubmit":"remote", "nv":0, "loadui":"enable", "toolbar":[ false, "" ], "scroll":false, "multiboxonly":false, "deselectAfterSort":true, "scrollrows":false, "autowidth":false, "scrollOffset":18, "cellLayout":5, "subGridWidth":20, "multiselectWidth":20, "gridview":false, "rownumWidth":25, "rownumbers":false, "pagerpos":"center", "recordpos":"right", "footerrow":false, "userDataOnFooter":false, "hoverrows":true, "altclass":"ui-priority-secondary", "viewsortcols":[ false, "vertical", true ], "resizeclass":"", "autoencode":false, "remapColumns":[], "ajaxGridOptions":{}, "direction":"ltr", "recordtext":"View {0} - {1} of {2}", "emptyrecords":"No records to view", "loadtext":"Loading...", "pgtext":"Page {0} of {1}", "toppager":true, "width":1234, "sortable":true, "id":"previewGrid", "keyIndex":false, "tblwidth":150, "disableClick":false, "_height":64, "_nvtd":[ 486, 20 ], "totaltime":26 }}