Can't build release configuration because of 'missing' references

I had a similar problem. Project builds fine in Debug mode but in Release mode some references were missing.

I found out, the dll's of the missing references were all located in the bin/debug folder. I moved them towards a neutral location, added them again to the project and the problem was solved.

As pointed out by Filburt. There were some broken reference paths in the project files. After correcting these paths, everything builds as expected.

Not sure how they got broken to begin with though. Any thoughts?