Check the repository list in your tablet's Application Manager. Following the RTCOMM Beta installation instructions will result in the creation of a new "maemo Extras" repository entry, and that entry will have a blank "Distribution" line.

When the "Distribution" line is left blank for a repository, the Application Manager will substitute in the version of the OS your tablet runs, in this case "Diablo". As RTCOMM Beta needs bits from maemo Extras "Chinook", this isn't very helpful.

As you go through the RTCOMM Beta installation instructions, watch what each step does. One of the .INSTALL files creates the unhelpful maemo Extras repository entry. After it does so, take a short break from following the instructions, and fix up Application Manager's repository list before proceeding. Either make sure you have only one "maemo Extras" entry that has "Chinook Diablo" on the Distribution line, or have two separate entries, "maemo Extras (Chinook)" and "maemo Extras (Diablo)", with corresponding "Chinook" and "Diablo" Distribution lines.