Can't restore to Ios5, blobs don't work the way they did with Ios4, once they stop signing a firmware, for the moment thats it, no one can return to that particular firmware.
Only choice you have it restore to latest firmware 5.0.1 and lose your jailbreak, or restore back to an Ios4 version that you have blobs for that can be jailbroken. You will need to wait likely until a tethered jb comes out for the upcoming Ios 5.1