Hi,
based on my experiences, you should start from a clean install, especially if you have older UP installed.
Backup config files (save control setup ones too, its under users).
Uninstall and delete everything, install IL2.
If you need UP, patch it up to 4.10.1 only, and then install UP 3.0 (+UP RC4 fix). UP is not compatible with 4.11 yet.
I also have a backup copy of a clean IL2 install patched to 4.10, which can speed up the reinstall process...:)