Save error 8800 on some computers but not others

I am setting up a script on 5 similar Macs in the office. All are running Mavericks and Photoshop CS6. The script works just fine on 2 of the Macs. But on 2 others (haven’t tried the 5th yet) the script crashes with the 8800 General Photoshop error.

It executes this line:

    var psdFile = new File(DLPFolder+"/"+UserInputFilename+".psd"); // adds ".psd" extension to name

Then it says the error is on this line while trying to save as Photoshop file:

    app.activeDocument.saveAs (psdFile, PhotoshopSaveOptions, false, Extension.LOWERCASE);

Does anyone have any ideas why this would happen on 2 of the Macs? I could accept it if it was on all of them.

Thanks