Did you by chance update your bootloader? MIUI roms(the new ones) require the new bootloader (NewBL). Look in the development forum and find the AIO Toolkit, it's on top, stickied.
Sent from my LG-P990 using xda app-developers app
"Many came and many left."
Device: LG Optimus 2X
Rom: Experimenting, but mostly Optix or TonyP's magic ROMs
LG GT540 Optimus
Apple iPhone 3G
LG Optimus 7
SE Xperia X10 Mini Pro