So you are able to telnet from the 10.75 network to the 10.80 network and vice versa, but your application is failing? What type of application are you trying to access on the remote network (ie what port are you trying to connect to?)
If you are able to telnet to the remote network, it sounds like routing is set up correctly so I'm not sure why you would want to map your network into the remote network.
A topology of your network and the relevant configs would help figure out what exactly isn't working and where the point of failure is.