Welcome to RPTools!
You're seeing the error messages that result when MapTool tries to convert the XML that is stored inside the RPTOK file and there's some kind of error (the RPTOK is just a ZIP file with a different filename extension).
Unfortunately, the XStream library that takes care of the conversion doesn't provide enough information to narrow down exactly what the problem is (there's no line number from the XML file, for example). The version of CT that you're using is the latest (you stated you're using 1.0.b12 and that is the most recent); otherwise I would've guessed at an incompatibility between an older version of one program and a newer version of another.
Sorry, I can't help more than that. Perhaps if you post again and attach your RPTOK file to the posting, someone here can take a look at see what the problem is?
Background information would be good, too: which OS, which version of Java, how much memory for MapTool, which version of MapTool, and so on.