Hello Joseph Doyle,
OpenAccess allows to use .pfx files for signing; I've just re-verified this. The only issue with password protected key files is, that the password must come from somewhere when the solution or project is compiled. For this, the key containers name is passed down to the enhancer with the keyContainer argument.
Please check that the OpenAccess enhanced assembly's project file is having the right signing settings. When the issue persists, please send us the content of the output window so that we can see what exactly goes wrong.
the Telerik team