Bob, did you want to upload a completey new texture then? If you want to use an existing texture you simply can put a link to it, shouldn't be a problem though?
You can also try to remove a few existing textures, and replace them with a link, and then try again.
I also tried to upload a texture just as a test and I got the same message.
Edit:
Mark wrote:Looks like it might just be us, Bob. I also wasn't able to send a texture attached to a private message and I'm at 1% of my quota.

The message says "Sorry, but the maximum filesize for
all Attachments is reached. Please contact the Board Administrator if you have questions."
So it's doesn't matter what's your personal quotum. Maybe it's just in the general forum settings, that there may be no more then xxx MB attachments in total.
Edit 2: I tried also to PM a texture as a test and then I got this message:
Sorry, but the maximum filesize for all Attachments is reached. Please contact the Board Administrator if you have questions.
Sorry, but the maximum filesize for all Attachments in your Private Message Folder has been reached. Please delete some of your received/sent Attachments.
Sorry, but the maximum filesize for all Attachments in the Private Message Folder of 'bob roest' has been reached. Please let him know, or wait until he/she has deleted some of his/her Attachments.