I had the same problem with playing PAL titles on my NTSC system when I first moved from Gamma 0.3 to Softmii..
1. It is NOT the hacks.ini option for FORCE DISC REGION. If everything with the softmii install was done right it is not needed.
2. The problem was that I followed the tutorial
too closely based on the instructions that if you have Starfall etc then you can skip to Section 3.
You need to start at Section 2 and follow it till then end. It is in section 2 that ARC (Any Region Changer) is run and patches are applied to the system that enable the region free functions.
3. Once I did this I had my hacks.ini loaded with all the Region 289 NTSC hacks and had Force Disc Region set to enabled I had another issue where starting a disc from my own region would boot to a black screen. (did not matter if it was an original or a backup) I went back in and disabled Force Disc Region and then everything including PAL discs was working perfectly.