Error: A reference to ''C:\tools\functions.dll' could not be added...

[Sacha Korell]

I am trying to set a reference to a 32 bit DLL that was compiled with Visual
Basic, to be able to access its functions, but I'm getting the following
error:

A reference to 'C:\tools\functions.dll' could not be added. This is not a
valid assembly or COM component. Only assemblies with extension 'dll' and
COM components can be referenced. Please make sure that the file is
accessible, and that it is a valid assembly or COM component."

I am using ASP.NET (VB.NET) in framework version 1.0.

Any ideas what the problem could be?

Thanks in advance,

Sacha