I had to reinstall Eclipse 3.7. I installed Findbugs plugin anew. After the first analysis, Findbugs asked me whether I want to switch to Findbugs perspective, I answered 'no'. When I tried to switch to this perspective later, I only got a perspective with no Findbugs explorer. Reinstalling only Findbugs did not fix the problem. Only a full reinstall of Eclipse 3.7 fixes the problem but I cannot do that once again. I tried to restore defaults in Findbugs setup in Eclipse preferences but it didn't solve anything.
N.B: This problem does not occur when you answer 'yes' after the first analysis.