Importing package - The System Has Encountered an Error

Hi guys, 

Getting an issue I've never faced before. I tried importing 19 objects from one of our environments to another. The inspection didn't show any issues, but after clicking import I get the following error:

It looks like all the updated objects have been updated successfully. There was one object which I imported, a new constant, which seems to be causing these problems. If I click to view its dependents or try to delete the constant in the environment I moved it to, I get this error message:

Any ideas what's causing this? There doesn't seem to be any issues with it in the original environment.

Thanks.