Sorry for posting to this old thread, but I have the same problem.
I downloaded the RBR Compendium from Jenolan's website. I imported the CDPs in the TS12 folder of the downloaded zip file to Trainz 12. The error message appeared only for one file, "Razorback Railway v6.3.cdp". I tried to extract the contents of that CDP file with CDP Explorer, but CDP Explorer threw error messages when I opened the CDP file in question (cannot be read after the end of the stream), though the contents were shown, as well as when I tried to extract the contents (Source array was not long enough. Check srcIndex and length, and the array's lower bounds.). I tried Firefox and Google Chrome for downloading, but the results were the same.
Are there any other ways to resolve this problem?