I'm having the same problem, I don't get it at all. I bought my Xperia Mini Pro (SK17i) yesterday and so far I have been only able to flash stock rom and MiniCMSandwich AOSP Android 4.0.4 RC3, both of which work fine.
With all other roms I get stuck on the logo (depending on kernel - Sony, Sony Ericsson or Free Xperia logo). I do full wipe, dalvik cache etc. but nothing helps.
So far I tried: FXP 117 7.2.0, FXP 117 9.0.0 and XROM ICS RC7.
I tried different basebands, flashing in different order etc., no matter what I get stuck on the logo.
Could someone post a detailed step-by-step instruction how to flash either FXP or the XROM on the Mini Pro? Which baseband should I use (and how do I know it's the baseband's fault when the rom doesn't work), what about Wi-Fi etc.
I flashed Galaxy S+ (I9001) before and didn't have any of these issues.