You might try reposting your question to the fsharp-opensource mailing list. That's where most of the collaboration around F# on Mono takes place, so you might have better luck getting an answer there.
A couple of quick suggestions to try first though:
- The April 2011 F# CTP is way out of date now. Try installing F# directly from the open source F# repository instead -- it includes a number of installation fixes and minor patches that make the F# compiler (and F# interactive) work better on Mono.
- The PowerPack is also quite out of date at this point. Once you've built/installed F# from sources (above), you might try building the PowerPack from sources too to see if that fixes the problem for you.