The IDE insists that all projects in a workspace must be in the same "mode" (Debug/Release/...). If not, things will get really weird.
If you import projects with different "modes" you get into a mixed state, which sounds like your problem.
The easy fix is just to select a mode from the combobox on the toolbar. The IDE will select this mode for all projects (assuming all projects have this mode!).
Use "View" -> "Target files" to check the mode for each project. At the end of each project is should normally say "(Debug)" or "(Release)". If it just says "()" something is wrong. Do the above easy fix.
