The "Error 500" is a very general error. There are several reasons to get this error. You will get this error when you are trying to delete the "Instant Upload" album, or trying to look at someone else's albums via a link you received, or trying to share invites, or trying to login on picasaweb.google.com, or change the properties of an album, or trying to use the account migration tool.
To solve this error, clear your browser cache and clear the Google cookies inyour browser. If you have reached the maximum number of invitations which are allowed within a 24 hour window, then wait for 24 hours and then try again to share invitees. Picasa does not allows you to delete the "Instant Upload" album, so do not try to delete it.
Quick Tip to Backup your Digital Photos
If you have treasured photographs, or you take photos of everything you like, you won't want to lose them. So, what is the best way to backup photos on an ongoing basis? In the back of your mind, you know you need to backup all of your photos. But where do you start? Here's how to backup your digital life: PicBackMan is the easiest and simplest way to keep your videos safely backed up in one or more online accounts. Simply download PicBackMan (it's free!), register your account, connect to your online store and tell PicBackMan where your videos are - PicBackMan does the rest, automatically. It bulk uploads all videos and keeps looking for new ones and uploads those too. You don't have to ever touch it.