EV search query problem

Dear Experts!

Our customer is using EV 12.04 with FSA archiving.
Archiving task is completed, but if we want to browse
the search ui on the admin console interface we got the following error:
- Cannot make a search query

The same error occured with the Internet Explorer too.
When i login to the search gui i can see the folders, but i cannot
see the files. IIS is running fine. 

Question:
----------
- What causes this error?
- How can we fix it?

Thanks in advance! 

BR:
Pali