Debugger hangs in thread after breakpoint

In one of my Visual studio 2005 projects, i'm using a thread that perform some actions.

After successfully stopping on a breakpoint on the first instruction that is to be executed by the thread, when trying to press F5/F10/F11 to step into the code, nothing happens and the application acts like the thread doesn't execute anymore. The next instruction is never reached and no exception is fired. I can reproduce this error by putting a breakpoint anywhere in the thread then pressing F5/F10/F11.

This is quite strange since i've another project in the same solution that uses the same techniques and this other project isn't affected by this strange behavior.

Any advice would be welcome.

EDIT : This problem disappears from time to time : yesterday it didn't occured, this morning it did, and since a few minutes it doesn't anymore...