As I'm compiling Slicer, the compiler returns error messages for various files.

This is probably because your source code is not in sync with the latest version in CVS. For example, someone may be uploading new functionality and may not be finished. Or, someone may have introduced errors into the package.
Wait a day, and then download new source from the CVS archive and try compiling again.
Or, you can post a message to the Slicer developer's list. Include the operating system and compiler versions that you are using, as well as a copy of the compilation errors that you are seeing. You should receive an answer soon.