aah found it
My solution of the error was to remove content of App_Data\Index folder, restart the application (by a change of web.config) and execute indexing in the 'secret' interface: http://sitehost/EPiServer/CMS/Admin/IndexContent.aspx
I also "delete from tblIndexRequestLog"
Im getting a lot of these error since 2 days back:
There is 441592 rows in tblIndexRequestLog
My config is:
The files under datapath\index are two days old.