The resource file is not valid. Overwrite it with a new empty one dialogue is when the program aims to open a FOXUSER.DBF and FPT file in the root application directory

This is most likely an access rights issue. 

The first thing to check is whether it's a rights issue or not (this example will be focused on the IT department to follow), to do this, ensure the user who launches the P11D Organiser has read, write and execute permissions recursively from the /P11D/ directory downwards. 

In the most likely case, the P11D Organiser will be located on a server, and the user access this from a shortcut on their desktop pointing to a UNC path, i.e. "\\server\share\P11D"

The user will either be a standalone user, or more than likely in a group within active directory. Ensure they have full access, for instance:

You may then either need the user to reboot the machine, or force a group policy update, for instance: