TREX search engine error

Hi,

I am new to KM.I installed TREX server in separate Host.I am accessing the TREX server into our portal.I created the Web Respository and craeted Crawler and Index.When i check the TREX monitor and Crawler monitor everything running fine.But when i am Searching the content throough search engine i am getting the following error.

<b>Search Failure

com.sapportals.wcm.WcmException: Index does not exist; indexId = "test_index" (Errorcode 7)

An unexpected severe error occurred during the search call. If the situation persists, inform your system administrator.

</b>

Can anyone suggest me where exactly i am getting the problem and need solution.

Regards

Usman