Interesting problem:  I always use library functions in .NET apps to maximize code reuse, especially for Data Access calls.  So when I ran across the following error from Oracle when connecting to a server running 10.2, I was stymied.  Especially since it worked fine with a 10.1 server:

 

ORA-12571: TNS:packet writer failure

Looking this one up brings a whole lot of results, none of them helpful in this situation.  To make it worse, VS2005 ran the application just fine. 

The solution?  The server had the 8.1 connector installed, which for some reason connects to 10.1 just fine.  10.2 was different enough to through the error above.  We got IS to push the 10.2 client on the server, and everything is working.