How come when i try to install the SWAT 4 patch it says that an existing copy doesn't exist?

Ok so i just recently bought SWAT 4 and SWAT 4 the Stetchkov syndicate. SWAT 4 installed fine except everything is labeled as COMPANY_SHORT_NAME/PRODUCT_NAME or something along those lines. It runs fine as well. However, when i try installing the patch/ the Stechkov syndicate it starts the installation process but then a error box that says "An existing copy of SWAT 4 was not located on this computer" I have no idea what's going on, i tried renaming some of the files when re-installed SWAT 4 but that did nothing. So any ideas what's causing this/how to fix it?