Here's the latest: I was hosting the older files on Switchpod. All the newer files are on my LibSyn account. Switchpod, as best I can determine, was purchased by LibSyn. LibSyn migrated paid accounts over but my account was a free one and was simply discontinued. I wrote to LibSyn and they kindly migrated all my files over this morning. Yay, LibSyn--you guys rock!!!
Now, all that's left is to go through and update the file locations behind the links and it's all done. I'll keep ya posted!