[AnotherOne]

My son has a Lumia 800 and he just told me he set an 11 digit passcode, but the homescreen only allows the first four and then blocks access for increasing length of time. The manual says the passcode has to be at least 4 numbers. I've tried the last four numbers in the passcode he told me and the same happens: after the fourth number the homescreen locks. So it's not about the fourth number being wrong, it seems to be that no matter what the passcode is, it locks after you punch the fourth number. 

Any ideas or own experiences before I do a factory reset? 

[paulheu]

In all honesty it sounds to me he actually used a 4 digit code and can't remember it now. A Nokia Care Point will be able to help you with this, but you will need proof of purchase and all data on the phone which is not synced or backed up will be lost.