I\'ve also recently run into this problem (specifically, a forrtl error not being able to write to a pipe_dummy file in the climateprediction.net data dir) and seem to have resolved it (so far...). Basically, even after quitting BOINC manager, there were still a couple hadxxx processes still running (as seen in Task Manager on WinXP). No idea how they were left behind but killing them allowed me to do a rename on the pipe_dummy file, something I could not do before that (I\'d get a \"file in use\" message). There was also what looked like an orphan BOINC Tray Manager (I think) process which I also killed, but my money is on the hadxxx processes. (Note that \"hadxxx\" is supposed to be shorthand for something like hadsm3_6.07_windows_intelx86.exe.) After undoing the rename and restarting BOINC, the task resumed w/o any runtime errors.
This is certainly not the answer to all the variations of this problem that I\'ve seen here, but I haven\'t seen this answer so I figured I\'d share.