Appearance Editor says Theme doesn’t exist yet i’ve worked on it for three weeks

I updated to 2.9 this morning. I then also tried to update the (fluid) Stylesheet to change some color treatments. When I clicked “Update File” on the Stylesheet editing page, I got the message “Theme doesn’t exist!” So now I cannot update the appearance nor can I get to the php templates.

Meanwhile, the Dashboard is allowing me to add subcategories to parents and to remove pre-existing subcategories, but the new subcategories are not showing up in the hover state of the menu tabs. I realize that servers might be slow on the wordpress.com side, but I’m also wondering if this is related to the Appearance Editor problem.

How to I either restore the Stylesheet and/or gain access to it? I’ve put a help ticket in to workpress.com but I’m trying to get the work done ASAP. Thanks for any help you can provide.