Method X in type Y from assembly Z does not have an implementation

[Laquesis]

What?:
I'm getting this:
"Method 'CreateObject' in type
'Microsoft.Practices.EnterpriseLibrary.Data.DatabaseCustomFactory' from
assembly 'Microsoft.Practices.EnterpriseLibrary.Data, Version=2.0.0.0,
Culture=neutral, PublicKeyToken=ab318854814bb523' does not have an
implementation."

How?
My WebService is accesing my database via the
Microsoft.Practices.EnterpriseLibrary.Data. Everything works fine when I run
my Application and WebService locally, but when I publish the WS to the
Server and do a simple Browse from the IIS the WS starts and when the code
reaches the point where the database must be accessed I get that error.
I've tried several things including publishing the WS to a fresh clean IIS
Server where there's only one Microsoft.Practices.EnterpriseLibrary.Data.dll
(the one copied by my WS publication). And that's the exact version of the
DLL. I also checked the Dll with the ildasm.exe in the WS Server and the
method CreateObject is actually there.

Why?
I don't know what's going on.
Any help will be greatly appreciated.

FJ.