It did stop working. I don't know what else to say. I am willing to work with you to get this figured out, but I highly doubt that it was a coincidence that two sites on two different servers failed to generate the sitemap and failed in the same way. Then this morning everything is fine and I didn't change or do anything other than try and generate a script and everything worked. The sites that the sitemaps were being generated on were all functional last night when these failures happened.
I hope this information helps to point you in a direction that identifies the problem so it doesn't happen again.