Startup disk full even though iphoto library backed up and deleted

Hi

When I startup my macbook air I got a message that my startup disk was nearly full.

I copied by iphoto library to an external back up drive and then deleted the iphoto library on my hard disk.

I emptied the trash and all looked fine as it freed up space.

Then next day, I started my laptop once again and the startup disk full message reappeared. I check the size of my HD and to my surprise, it looked full again. I check the iphoto library on my hard drive and it is indeed still gone.

Can you help?

Thanks

Peter