Struggling with my 50 1.4

I bought this lens a couple months ago to replace my nifty 50, which I wanted to use for low-light photography (think pub crawl, evening with friends, etc.) but had terrible focus issues in low light. I had the first opportunity to give it a serious whirl recently, and I failed to bring back even one sharp picture.

This isn't a 'is my lens soft' thread, as it performed decently in good light. There I was, trying to get a shot off in a dimly-lit area, f/1.4 about 10ft from my subject, and the lens would not focus properly, even using only the center AF point and not recomposing. Interestingly the lens had been micro-adjusted to -8 (using Reikan FoCal) but the next day, taking another few test shots, I realized it seemed to perform much better if I left it at zero micro-adjustment. I don't know whether the first micro-adjust failed or if somehow the lens changed since - it didn't get banged up or anything, that's for sure.

I know I probably need to run a few more tests, but I'd like some help narrowing it down. Was I using it wrong? Does it sound like the lens is defective? Was I asking too much of it? Are there any focus inconsistency issues on this lens that I should know about?

I don't know about the 1.4, but my 1.8 doesn't fare very well in low-light situations, either. It may be too cumbersome, I'd rather not do it, but you could try using the focus assist beam from a 430 EX II to help it, without using the flash I mean.

armis wrote in post #14623575
micro-adjusted to -8 (using Reikan FoCal) but the next day, taking another few test shots, I realized it seemed to perform much better if I left it at zero micro-adjustment.

This is not uncommon, it has happened to me a few times with various lenses.
Micro focus adjust only works for the distance that you are set up for at the time and if you do the set-up too close it can be wrong at other distances.

To do micro adjust sucessfully you need to carry it out at various distances and under various lighting conditions, each time taking multiple shots, then follow it up with a field test.

Lighting can affect things drastically and I have found the best results for micro adjust are obtained outdoors in overcast conditions.