Version 1.63 is the latest patch - this is good news, as it means you are now up-to-date.
You should be able to go ahead and install your stuff pack.
If you encounter further problems, it may be a question of doing a completely fresh installation. It is horrible when this happens because it can take a long time. However I usually just make a large pot of tea and listen to some music while it's going on. I would recommend doing a clean uninstall, then installing the base game and patching it (to 1.63), then each EP or SP in order of release, running any updates that turn up as they appear.
But hopefully you will not need to resort to reinstalling.
Fingers crossed for you.
