jQuery Grid Plugin - jqGrid

I'm traying to import grid's configuration from a xml file , all works fine when  at least i have two columns on the grid, but the problem is when i have only one colimn on the grid, I recive a message "Length of colNames <> colModel or 0!"

this is part of the xml file

......

<pager>#pgr_population</pager>

<pgbuttons>true</pgbuttons>

<pginput>true</pginput>

 <colModel>

<name>concept1</name>

<index>concept1</index>

<width>400</width>

<align>left</align>

<editable>true</editable>

<editoptions>

<size>80</size>

<maxlength>160</maxlength>

</editoptions>

<resizable>true</resizable>

 </colModel> 

 <rowList>10</rowList>

 <rowList>20</rowList>

 <rowList>30</rowList>

 <colNames>POPULATION</colNames> 

<sortorder>desc</sortorder>

............

And this is a part of the server response

......

<rows>

<page/>

<total>2</total>

<records>17</records>

<row id="9387">

<cell>COATEPEC</cell>

</row>

<row id="9401">

<cell>ZIMPIZAHUA</cell>

</row>

<row id="9402">

<cell>TEOCELO</cell>

</row>

</rows>

.....

Dou you have any ide whats is wrong????

I hope you can understand my question I'dont write the english very well