Hi bis010. I have the exact same problem you have.
In fact, i have been trying to catch up on a number of shows over the last week (Christmas holidays ) I will watch and then delete approximately 4 hours worth of recorded shows, then I get the menu hanging on deleting. In fact, I've had to reboot the Nextbox 3 over 6 times so far in the last week.
Called Rogers tech support, they could not see any errors. They verified I am at the latest software levels. The tech guy told me he's never heard of this issue and basically told me to go swap the box. That's fine if you rent the device, not so easy if you own it.
That said, this is my second Nextbox 3. I swapped the first one because of this same error. I have also seen it on the Nextbox 2 as well. (which is one of the original reasons I went to the Nextbox 3).
I wonder if this problem happens with a lot of recording/deleting activity. Maybe there is some corruption on the internal disk. I asked and was told, if you go through the menus and Reset the box to factory settings, under Troubleshooting, it actually does a format of the disk. Does anyone know if this is true? If so, I might try that and see if it helps, even if it means losing some of my recored shows.
It kind of formats it.. i wouldnt say a FULL format per say.. but the closest you can do to it... at least removes bad recordings.
We record & watch about 5 things at least a night. We DONT get the deleting lockups though. But, we usually watch, let finish, delete. Start up next one.. repeat. (all while its usually recording other stuff). And dont seem to have the issue.