If this would be really the issue with media type then EMC would need to fix it thus the best bet is support case. This is not new and EMC should be aware of it - same happened to people who would use LTO3, but it was configured as LTO2. NW would not automatically relabel LTO2 until you would not label it (and thus mark it as LTO3 media). I never paid attention back then what was the issue as workaround was simple, but here we have now different story.

When you say NW refuses to mount, can you tell me what happens when you manually try to mount the requested tape?