you will need to flash a new SBFusing RSD lite.
I used this SBF http://www.multiupload.nl/I52KOPDS8N
It should work unless you have flashed a higher version before hand. If you have installed a higher version then try these SBF and use one the same version you flashed before.
Yes if you are installing ICS and following the defy+ guide dont flash the CM9 kernel.
If you want to install ICS then use this ROM http://defy-cm.net/CM9-NIGHTLY-120417-Defy+.zip
Its the new epsylon one as I heard the Quarx has a few more issues not sure if the new build has sorted it out,
You can use the latest version of gapps found here http://goo.im/gapps/gapps-ics-20120422-signed.zip
Follow these instructions using the rom and gapps I linked but skip the flash CM9 kernel
A How to on flashing ICS(Defy Plus Builds)
1:Head over to Stable Recovery from boot menu
2:Wipe Data (Nandroid Backup Before Doing this [optional])
3:Install Zip from SD
4:Select ur ICS(DefyPlus) zip
6:Flash CM9 Kernel (SKiP THIS STEP!)
7:Flash Gapps zip(On first page of ICS DeV thread)
8:Clear Cache and Dalvik Cache