I don't honestly know why that error is occurring you are the 5th that i heard of. It either has to do with a newer version of the kernel being replaced or a newer firmware version that is incompatible with the kernel settings.
As for setting it depends on your firmware. The easiest would probably be redoing all the steps to the initial set-up of OtherOs.
If you get another chance at it try to double check/cross-reference what you typed for kboot.conf, wish I could figure it out myself, but am not changing a thing on my end because of the off chance I too lose UDF 2.5 support.