Invalid DLL call from VB.NET app

[Steve Covert]

I have a VB.NET Winform app calling a VB.NET DLL which works 99% of the
time.
However, in a few cases, an error results from the dll call: "The format of
the file MyDll.dll is invalid."
The error object error number is 5.
Has anyone run across this?

A thousand thanks.
SC