Hi, guys,
So, I have talked to SAP and after a few tries, we've come up with a solution.
It was a guess, even for the SAP analyst, but it worked and that is all that matters.
I've downloaded the WPFToolKit.dll file, and I copied it in the folder
"C:\Program Files (x86)\Sybase\PowerBuilder 12.5\DotNET\bin"
After that, I have added a referenced inside my WCF target.
It worked!