Sam,
I felt compelled to suggest an answer to this one, despite the excellent replies to this post. Richard, Victoria and Jonathan are all on the same page, and from what I can tell, it's definitely the right page - no one marked a suggested answer, so there is no way to confirm the solution.
You likely do not have a Form (GP Window) customization. Please check the pointer in the Dynamics.Set file on all workstations, to ensure this is indeed the case. Check each pointer location for a Forms.dic file. Checking customization maintenance on one workstation will be insufficient, because various workstations can have completely separate configurations.
The likely reason the Dynamics.Set file points to a shared location on a server, is your parnter/predecessor were being thorough about the their configuration settings, ensuring any customization created using Modifier would be available to any GP user.
Once you've validated you have no customization, set the pointer in the Dynamics.set file to the default location in each workstation would save overhead caused by GP checking the server location for an absent file every time it starts.