If you are checking in from Windows, check if your code does not have those invisible ^M characters -- editors in UNIX often give errors/warnings 'cause of that.

Also try and replace tabs -- different users will end up seeing tabstops differently some with 4 spaces, some 8 and not good for code readability.

Best approach IMHO is to have a pre-defined script check your code against the coding guidelines of your organization. Loads of source control systems have this functionality.