NOTE for anyone using GUIMiner with poclbm

You probably noticed that GUIMiner poclbm recently started failing semi-silently (the GPU still does hashes at the normal rate, but nothing gets submitted so the accepted count stays at 0). You can see the beginning of an error message when the miner is started if you have the "console" on.

A bit of research led to threads 1 and 2 pointing to an issue with poclbm, and that there is in fact a fix on git, but no windows binary nor an update to GUIMiner. Apparently the problem is not present in the latest "official" build of poclbm, so reverting to that will fix the issue.

Rather than using an older version of GUIMiner, you may want to only downgrade poclbm, but it's not quite as simple as replacing one file.

To manually fix your GUIMiner, download the 20110709 file at https://github.com/m0mchil/poclbm/downloads and extract it to some folder (e.g. 'new-poclbm'). Now, find the "library.zip" in the GUIMiner folder and extract it to its own folder (e.g. 'old-library'). Then extract the "library.zip" from the poclbm download on top of this one, overwriting and adding new files. Recompress the files as a new "library.zip" and put that in the GUIMiner folder (you may want to save the old one under a new name before replacing it!). Make sure that the "library.zip" you create contains the files from 'old-library' at the top level (that is, not inside a directory called 'old-library').

Then copy-and-paste all the files other than library.zip from the poclbm download into the GUIMiner directory.

This worked for me, and hopefully works for you.