"Change Disk..." in Time Machine stays grey
I've been using two (identical) external FW400 HDs for backing up two (identical) Macmini's that we have in the house, backing up both Macmini's onto both HDs satisfactorily for the last 3,5 years or so. Today backing up MacMini A and B onto HD#1 went fine, then I couldn't "Change Disk..." (to backup onto HD#2 on MM-A anymore (stayed 'grey', so not 'clickable'), but could still "Change Disk..." on MM-B.
So now I'm 'stuck' with using only HD#1 for MM-A as it still 'recognizes the last used backup drive, I suppose, because eventhough I cannot click "Change Disk..." anymore I can still backup onto HD#1 by rightclicking the TimeMachine ico and then clicking "Backup Now". On MM-2 I can still use both HDs.
Does anyone have a tip how to make "Change Disk..." work again on MM-A? (I did disconnect and unplug the ext HD, with its own power supply, and then restart MM-A and then reconnect the ext HD, but to no avail)
Mac mini, Mac OS X (10.5.8), mid-2007 model (2GB RAM, 120 GB HD)