Version 9.1.1 implemented the .Net 4.0 framework, which has different security than previous versions of the .net framework. In particular, it won't default load an assembly on a remote machine (and in some cases, won't even load one that came from a remote machine, but is now local).
Previous .Net versions did not have such a security restriction which is why earlier Runtime versions do not have a problem.
To allow loading of remote assemblies requires the creation of a .Net configuration filenamed wrun32.exe.config in the same directory as wrun32.exe, with the following contents:
(Note that if you have renamed the Runtime the configuration file name must correspond.)