Ok, I found this one. For some kind of reason, I accidentally hit the quote key which has dropped that character at the end of a function when viewing the Web Service PRG source. So, later on, I recompiled it for something else and then the additional character was then part of the PRG. What is a coincidence is that is ended up right after the quote of a parameter which made it a quote after a quote. So, the SOAP client received a custom message in regards to that but it took me a while to figure it out as I knew I didn't touch that specific function for a while.