Try moving the entire installation to a different folder. (Try one fewer directories deep into the filesystem, and with no non-English characters. If all else fails, C:\SRB2\) Also make sure you're actually running the game from the same directory as it's contained in. (Just double-clicking the EXE does this, so it should only be a problem if you're using a weird setup to launch the game)
If that doesn't work, try redownloading the installer (it might've gotten corrupted in the download process) and re-extracting the game files. If that still doesn't work, then uh... post the contents of log.txt (if the game creates it; I don't quite know what order the different startup functions are executed in) and we'll try to help further.