SharePoint Search Crawl not working (This item could not be crawled because the repository did not respond)

Hi,

My Environment is a six server SharePoint 2010 Farm. 2 Apps, 4 WFEs. Database is a SQL Failover Cluster with 2 Nodes. Patch June 2012 CU. Search Service Application is on the first App Server.

We're hosting one Webapplication with a SSL URL for internal and external use.

Days ago, everything works fine, but actually, the crawl doesn't function anymore. Everytime I start a crawl, I get the following error:

"This item could not be crawled because the repository did not respond within the specified timeout period. Try to crawl the repository at a later time, or increase the timeout value on the Proxy and Timeout page in search administration. You might also want to crawl this repository during off-peak usage times. (Error from SharePoint site: WebExceptionStatus Timeout The operation has timed out)"

Till now I tried the following:

1. Increment Crawl, Full Crawl, Index Reset + Crawl > Getting the error above
2. Disableloopbackcheck > Already done
3. Switch Search Service Account to fully priviliged Farm Account > still the error
4. Search Service Accounts has rights to Content Databases and so on? > yes
5. Search Service Account is not deactivated, has the right password and so on > yes
6. Opening IE with Search Service Account on Service and try to open the Sites to crawl > works
7. Recreate Search Service Application > still the error
8. Recreate Search Service Application on other App Server > still the error
9. Fixing "Unknown SQL Exception 2812 occurred." Reinitialise Usage and Health Data Collection + IISReset + sptimerv4 reset > still the crawl error
10. Is the Sharepoint Server Search Service running? > yes

Do you have some more ideas what I can check?

This Problem is really frustrating.

With kind regards,

Tim