Undescriptive Xcode Error

I am having some weird errors coming out of xcode. The latest is here:

I am not sure what to make of this error. What is interesting is that if make any changes to the code or clean the project the build will succeed the first time around, but fail the second. Also, it will succeed every time if I close the editor, but will fail immediately if I have it open.
I would post some code, but it is a very large project and I’m not sure where the error is being generated.

A summary of my project: I am downloading a .pak file from a server, then applying a material inside it to a pawn.
Has anyone seen an error like this and have any insight on it?