Like Elwino2.3 said you need to flash the nAa kernel using flashtool.
But before that you need to unlock your bootloader than flash the kernel.
Please re-read the thread carefully where you got the MiniCm7-2.2.0 ROM.
All necessary details are provided.
Don't worry it also happened to me. I got too confident coz i had flashed many other ROM's and so i just flashed the ROM without reading the instruction.
You either use Sony Ericsson Update Service to reset your phone back to the stock sony ericsson rom or you can try to directly flash the kernel.
As for myself i used the Update Service coz i thought that it was more safe.
X10 mini pro running on
MiniCM7 and nAa kernel
Samsung Galaxy Pocket running MAK-DROID V3