Passing visual studio webtests fail in test explorer

Question

I have a web performance and load testing project which executes as epected when I open the test definition and hit run however fails when i run through test explorer.

I have narrowed this down to only tests which reference another project in the solution (utilities project for custom validators).

when running tests via test explorer it errors with Request failed: Could not load file or assembly 'PerformanceTestingUtilities, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified. However works fine if I open the test and hit run.

What could be causing this to happen? I get no errors on build and nothing in the output.