Recording turns off by itself

I have a Sansa Clip+ 4GB and like it very much.  It plays very well and when it records it records superbly.

However, when I want to record a class, I start it recording, lay it upside down so that the microphone is pointing to the sound source.

I come back later, and find the whole player turned of, and when I go to play the recording, it is only a few minutes long, while the class was an hour long.

Am I doing something wrong?

Do you have the Sleep option turned on, so it will shut off after a certain period of time?

Do you have enough free space (internal memory) to record for the full hour? These things record in WAV format so they do use up a lot of memory space for recording.

You are exactly correct!  There was no room for the recording.  You hit the nail on the head.

Sorry it took me so long to reply.  My Sansa Clip + was indeed full.  It took a while to make room.  I bought  a micro SD card (on black Friday) and moved most there.  With about 3 GB free, I made an hour and half recording.  

Thank you very much!