have original ipad which won't backup, itunes says there is an error but won't give me any details

I have an original ipad which I struggled to update the OS software from 3.2 to 5.0 but eventually managed to do this manually. HOwever, now there is an update to 5.1 which when I try to do it via wifi, it just says there is an error. Tried to do it through iTunes but it starts to back up and then tells me there is an error but does not give details, when I click on the further information button it doesn't do anything. Because it won't back up, it won't let me install the update. It won't back up either to the computer or to iCloud, I have tried both. I would be grateful if anyone has any ideas.

Also, in case anyone can help - several of my apps won't work on my ipad - logo quiz, ibooks (worked fine until I updated software system) and a few others - just flicks on briefly and then throws me out.

Thanks in advance.