So there's no need to use a component or exe like FFSJ to join files. Windows can do it using a CMD command prompt.

For example:
cd c:\websites\mywebsite\data\encrypted\ && copy/b encrypted.001 +encrypted.002 +encrypted.003 +encrypted.004 +encrypted.005 +encrypted.006 +encrypted.007 +encrypted.008 +encrypted.009 +encrypted.010 encrypted.rar

This will join encrypted.001 to encrypted.010 and save it as encrypted.rar, it's fairly fast and not CPU or Memory heavy at all.

This works fine when run in the standard CMD, but when trying to run it from code using WScript.Shell I get a '80070002' permission denied error.

User permissions to the folder containing the files are all correct (to my knowledge), any suggestions?

Thanks