I'm using Infragistcis NetAdvantage V8.1. I'm deploying to a Medium trust environment, and no  matter which version of the Infragistics assemblies I use (out of the box, APTCA, APTCA signed), I always get this error:

Could not load file or assembly 'Infragistics2.WebUI.UltraWebGrid.v8.1' or one of its dependencies. Strong name signature could not be verified.  The assembly may have been tampered with, or it was delay signed but not fully signed with the correct private key. (Exception from HRESULT: 0x80131045) .

I've deleted the assembly on the hosting server, re-uploaded every time, double checked that the ftp transfer was in binary mode, used every version of the UltraWebGrid Assembly which is available to me, but nothing changes the error message. 

I've even tried following the instructions in Tony Lombardo;s blog to remove the string naming using ILMerge, but that only makes matters worse, becase the app wil not then compile.

 Can anyone suggest what I can do to fix this, becasue having followed the Infragistics documented instructions exactly, I'm pretty much out of ideas?

Thanks in advance

Mike