References not found

问题

I have multiple projects in my solution and currently I am experiencing a very weird problem:

I have project A - rebuildable with no error. I have project B referencing project A - also rebuildable with no error. But when i try to rebuild all, the whole solution with othre projects except A and B it gives me errors:

Error 31  The type or namespace name 'Something' could not be found (are you missing a using directive or an assembly reference?)

And errors are not just in projects A or B, but all over the solution..

but when I comment in project B all the objects created from classes from project A ( and the project A is still referenced in project B) - it all works.

Any idea what may be causing such a strange problem?

thank you