I have had issues with our TS2900 library before. I have never rebooted our system to recover though. I have had to reboot the tape library. But sounds like your real issues is you somehow upgraded the micro code on your FSP to a level that is greater than your HMC.
Can you browse to your FSP to check the level? Second check to make sure you apply FSP microcode via the HMC and not via PTFs. This is usually how one gets out of sync.
Before updating your FSP, HMC, or OS you need to verify the currnet values of each.
1. What is the FSP min level for the OS upgrade? Do you need to need to upgrade your FSP? If so stop and check HMC version.
2. What is the FSP levels support by your current HMC version? What version of the HMC can you upgrade to with your current FSP version?
So really you want to upgrade HMC, then FSP, then OS. The HMC talks to the FSP and the FSP talks with the partitions.