If you find the following in your SQL server event log:

SQL Server Scheduled Job 'Start_Incremental on Companyname_MSCRM.ftcat_documentindex.[7.5]' (0xB7324B3916DFFF449C956936187A787A) - Status: Failed - Invoked on: 2006-08-09 13:01:21 - Message: The job failed. The Job was invoked by User <user>. The last step to run was step 1 (Full-Text Indexing).

Make sure the Indexing service is running on the server.

Run execute sp_fulltext_database 'enable' in SQL Analyzer against the Companyname_MSCDM database.