I have had this issue before but I don't know if I ever found a solution to it or if I just forgot what it was.

We are using Umbraco 7.2.2.
In our 'Scripts' (Javascript) folder, we have a few subfolders (myfolder/myscript.js).
When I try to add a new JS file to a subfolder through the backoffice and try to save the file AFTER adding some Javascript I get a permissions message and can save

File not saved: file could not be saved. Please check file permissions

I go to other JS files in the subfolder and save them, and they save fine. It is just when I tried to make new files. I checked the permissions through IIS and Permissions on to the folder, and I don't really see any differences between the files that were already out there and the files I just made through the BackOffice.

We added some new DLLs by manually copying them over from our dev to test evironment.

I tried changing the version on in the ClientDependencies.config file, but this still did not seem to be the issue.

If I take all the Javascript code out of the file and try to save the empty file, the save works. The Javascript file I have is a little over 8000 lines un-minified. Is there a line limit to Javascript file sizes in Umbraco? Or is this IIS?

Any suggestions to what this could be?