Window XP does not allow deleting files as those are being used by another program. I have tried to restart the software, but it is still impossible to delete TIFF files processed by Capture One.
You should be able to delete any file on your computer that is not a 'Read Only' file. This file must also be in the location you have permission to access.
Windows may be accessing files with another program. To confirm, launch the Task Manager (press Control+Alt+Delete and navigate to the Task Manager) and verify that no other program is running under the Applications tab.
In some cases, Windows Raw Viewer can lock up the TIFF files. Windows Raw Viewer may become the default program for image files processed in Capture One. After removing the Windows Raw Viewer program, the TIFF files worked properly again.
If a browsing window has thumbnails or filmstrip set for viewing, then Windows will 'hang-onto' these files. Setting the window properties to List or Details will eliminate this conflict.