I was going to suggest getting the latest SSDT so I am curious if that fixed it.
I did find a few links of others having this same problem, not directly using SSDT, but using VS2010, which seems to be what is on your system:
http://www.sqlservercentral.com/Forums/Topic1329543-2799-1.aspx
http://www.sqlnotes.info/2012/04/27/deploy-clr-in-sql-server-2012/
Please let us know if you get this working.
Take care,
Solomon...
SQL# — https://SQLsharp.com/ ( SQLCLR library ofover 340 Functions and Procedures)
Sql Quantum Lift — https://SqlQuantumLift.com/ ( company )
Sql Quantum Leap — https://SqlQuantumLeap.com/ ( blog )
Info sites — Collations • Module Signing • SQLCLR