This only happens on some OMS files. Not all of them. The message I get is "this package cannot be installed with the current release installed in the printer". Current release what??

The OMS File could be damaged or may not have been written correctly. If it wasn't downloaded from the Media Locator site(https://www.printos.com/ml/#/medialocator) then it could be custom file/setting and not have all the required parameters to work. Make sure your chosen parameters are correct when downloading from the media locator. You can create a suitable profile using a generic media from the printer's substrate library as an initial starting point.