Internal F# error with F# 3.0 in Visual Studio 11 Developer Preview?

Question

I have installed the Developer Preview of the Visual Studio 11 along with F# 3.0. If I open a F# project it is opened with no warnings or errors and FSI starts normally, but as long as I start testing it by sending my code to FSI (via contextmenu -> "Send To Interactive") I immediately see the following error message:

Error FS0193: internal error: Value cannot be null 

If I fall back to VS2010 and F# 2.0 (I installed VS11 in parallel on the same machine) it works without any problem. Any suggestions?

EDIT: It is difficult to derive a minimal example for this error, but I found that a similar problem was reported on FPish here. Especially the cryptic message Parameter name: con.

I spent several hours trying to simplify my programm but I failed to identify the line where the code would fail. It looks as if there were some problems with type inferred from usage: it either complains that the type is too generic and not constrained or fails with the internal error if I add some usages to help F# determine the type. It happens only in a really complex context, simple type infererring cases work fine...

Answer 1

You could try sending this as a bug report to fsbugs at microsoft dot com. (Thanks to Tomas Petricek for posting that e-mail address in a different answer.) I think that would be your best approach at this point.