Regarding the data mismatch warning you get..
"Are you getting a data mismatch error in the launcher? If so, it would have created a log file listing any files in the install folder which are not expected, as well as files in the Mods folder. To check this, if applicable, copy the following line into the location bar in Explorer and hit Enter: %LocalAppData%\Larian Studios\Launcher\Cache Then look for a text file named steam_<VersionNumber>_alteredFiles.txt (or similarly, starting with 'galaxy_', for the GOG version)."
See if there are log files created for you, maybe that could help you get a perspective over the issue?
