I've had my .NET clients talk successfully to .NET back-ends, Java back-ends, and Cobol wrappers with no problems, with security extensions, etc. all enabled.

I've had my .NET clients talk successfully to .NET back-ends, Java back-ends, and Cobol wrappers with no problems, with security extensions, etc. all enabled. But the key to that was having an active architecture group responsible for ensuring consistency across the organisation (libraries for each client platform host).