Message: "You don't have permission to modify files in this network location."

Windows displays this message when it is unable to save (or resave) your file.  Often the actual problem is quite different than you'd guess by the wording of that message (which comes from Windows and we cannot change). 

Resaving a file is trickier than you'd guess. We don't want to first delete the existing file and then save the new one. What would happen if Prism cannot complete the saving part? You'd lose the existing file. So when you resave a file, Prism tries to follow the following steps. 

1. Save the new file using a name something like ##.pzfx$.  The ## is replaced by the file name, and the extension depends on if you are saving in the pzf or pzfx format and which version of Prism you use, but always includes the $ symbol. 
2. Rename ##.pzfx$ to ##.pzfx. This step will delete the original file ##.pzfx . 

If your computer is set up so the permissions on the folder you are saving to does not allow Prism to rename files, then step 2 can not be completed, and WIndows displays the message about modifying files. In this case, your file has been saved as ##.pzfx$ or ##.pzf$.

Since the problem is one of folder permissions, change the permissions (settings)  to allow file reading and renaming (as well as writing) and you won't see this message again.