encrypted kubuntu stops the booting login process

[user1]

I am using lucid 10.04 on a hp laptop pavilion dv9000

I boot several times a day (I hope to preseve my laptop longer by 
stopping it between use).

It happens regularly that the boot login process stops after I have 
inserted the pass phrase, and then I have to reboot (ctrl+alt+delete) or 
restart to get logged into kubuntu.

I have experienced this during a long period, even when using 9.10 (as 
far as I remember).