Linda,
If you want a relatively large avatar, you can, for example, size it to 2 inches, (maximum dimension in either direction), but make sure that neither dimension exceeds 80 pixels, and the total image file size does not exceed 6 KB. Computers, as you are well aware, can be very unforgiving.
If it refuses to cooperate, feel free to e-mail me the photo, (in a large-enough file size that I have plenty of detail available to work with - it's easy to downsize an image, but impractical to upsize one, due to loss of quality), and I'll be happy to modify it, and upload it, and force the system to accept it.
I can, of course, increase the allowable file size for all avatars, if enough people want to do that, but I can't change it for individual avatars. The downside is that doing so would significantly increase the bandwidth used by this board, and slow down loading times for everyone, especially those with a slow connection. I'm always open to making changes, though, if it's for a popular cause.
Tex