problem with iphoto
I've upgraded my iphoto app but now can't open it. A message comes up saying I will need to upgrade my iphoto library to use new version of app but when I click on upgrade a further message says "Unable to write to library check that the volume has sufficient disk space." I then have only the option of quitting iphoto. I don't understand what is meant by the check volume message. I have plenty of storage space left on my mac. Any help appreciated.
iMac, Mac OS X (10.7.5)