The other possibility would be a corrupt CPD. The CPD is an
Access database used by RoboHelp to track and manage the project.
It somketimes uses its contact with reality and doesn't accept any
changes.
Try closing your project, make a backup, delete the file
<Projectnam>.cpd and open the project again. Expect to wait
some time, if your project is a large one. Now, try deletiong those
file again, and all shuld be ok.
Regards
---Dirk Bock