There are two possible problems:
1) You have a licensing issue, which I doubt, as I as involved with setting this up, or
2) you don't have the latest version configured to set the $MidasTempDirectory properly in your Notes.INI, so temp files are being created in your read only partition.
Please contact me directly (see contact details at http://www.GeniiSoft.com/showcase.nsf/ContactUs
) and I'll make sure you are set up correctly. The Midas Rich Text LSX will run on Citrix, but it takes a bit of configuration to get it right, due to the read-only nature of the default temp directory location.