UPDATE The supposed duplicate is a question on being stucking in \"Waiting For Debugger\" when executing Run, while this
Most of the times this is caused because of the overload of resources and threads over the emulator. Or even for the lock of objects that GC couldn't set free: http://developer.android.com/intl/pt-br/tools/debugging/index.html
Usually, a single restart of it will solve the issue, but sometimes it asks for the IDE restart, so be sure to make both tests.
Another good test is trying to start the app in "Start mode" and then try the debug mode again...
P.S: Don't forget to kill each debug process in the IDE after each test. This will prevent your env to be more overloaded.