The solution to this problem is to install the following Oracle patch:
Patch 11822454: DRG-10607 "INDEX META DATA IS NOT READY YET FOR QUEUING DML" SINCE 11.2.0.2 UPGR
This applies to errors such as these:
Failed to post DESSTEPS values
or
Failed to setValue for key 4 in table 'BUG' in project
or
Failed to setValue for key 4 in table 'BUG' in project
The issue occurs if you have the CTXAPP package installed on Oracle. This package is used by the Full Text Search feature in QC. The bug caused the CTXAPP package to not work properly with Schema Names longer than 29 characters.
Quality Center automatically chooses the schema name (by concatenating the <DOMAIN>_<PROJECT NAME>_db) up to a maximum limit of 30 characters. If the length is longer than 30 then QC will truncate it. Therefore if you wanted a shorter Schema Name you have to make sure the Project Name you entered was shorter than the Domain name plus a few underscores and the ending DB.
It is easier to install the above patch :)