I use LBC to start RDP-Sessions in the same way MichaelHerrmann does. So I have the problem too.
As I have a lot of RDP-Files, I wasn't very happy to create shortcuts to them. But as I missed it so much, I tried the suggested workaround with shortcuts. Sadly without success. I received the same error message as before.
The creation of many batch files was not an option and I decided to find a different solution.
After some investigation I found out, that LBC's quickdoclauncher.exe tries to find the shell open command for RDP.File in the registry. But this isn't possible, because for RDP.Files the shell command "connect" is used instead.
After adding the shell command "Open", LBC was able to launch my RDP-Sessions again. Hooray!!
In Win XP this can be achieved by using the file and folder options dialog. Simply create a new action "Open" by using the same entries as the default action "Connect".
In Win7, and I think in Vista too, this way can't be used any more. A big "thank you" to Redmond! The following way isn't very hard, but it changes the registry directly!!! Do this only, if you know what you are doing!!! Use it at your own risk!!!
I exported the corresponding registry entries under "HKEY_CLASSES_ROOT\RDP.File\shell\Connect" to a file, changed every "Connect" to "Open" in it and finally imported the file.
This is the content of the REG-File that I've used:
Windows Registry Editor Version 5.00