intermittant loading problem

i use sonar and keep my EWQLSO libraries on an external drive. the drive's letter was changed, but i then changed it back. when the libraries and samples are loaded in 1 project, they load and play fine. when i try to insert the synth in another project, there is no audio output.  then, when i go back to the first project where the loading and playing was fine, now it too puts out no audio. same thing when i then create a new project. now no audio output.  how can this be?   how can it work in a project, then not in another,which then seems to make it not work in any project after that, until i close somar and re-open?