Can't backup my iPad

Hi everyone! I have a sort of a massive problem, I can't back up my iPad.
My iPad 1 is currently jailbroken on IOS 5.0.1 and since I've been told that IOS 5.1.1 should fix some RAM problems that I'm currently experiencing I thought it would be best if I upgraded my IOS, (it's also untethred so I don't really have much to lose) but for some reason, I can't back up the content on my iPad on iTunes.
I plug it in, i go to my iPad then i go for "backup" but then it says that iTunes couldn't backup my iPad because (not my iPad) my BACKUP is damaged or not compatible with my iPad. I'm not sure what this means but I'd really need to back it up (I apologize because I'm not sure this is the exact translation as my iTunes is in italian, but it surely is a close one, maybe i used a word of too much but it shouldn't change the meaning).
Could it be related to the fact that (only when i reboot, either through SBsetings or normal reboot) all my apps are in the wrong place? There's no dock, all the apps are far away from each other and if i start one it shows as if it is an iPod app instead of iPad (the iPad kind of course, the iPod it shows as it should but instead of showing them in the center it shows them in the upper left corner), I can easily fix this by going into safe mode and getting out, no problem whatsoever after i do this (respiring doesn't work, same problem), I'm not an expert, that's why i'm asking here, I only thought it would be best to put all info.
Any help would really be appreciated, I know everyone here is more than kind so I'm sure you'll help me once again with this problem. Thanks for attention and in advance for your most precious help.

John

P.S. I backed it up^^ This is quite embarrassing sorry... I just had to delete some previously backups, I suppose there's a lmit of how many you can do.