At one point I changed the "Priority" Preferences to 1.0 (high)and generated a Google sitemap via Keylimetie's Sitemaps tab (after Spidering the website). Google's Webmaster tools gave me an error that the Priority tag was invalid, due to the "(high)" text within the XML sitemap.

Although I changed the priority back to 0.50 in Keylimetie, the XML sitemaps are still plugging the 1.0 (high) priority into some URLs. Any ideas how to correct this problem?

I was able to edit the sitemap in MS Word 2003 to remove the "(high)" text and Google accepted the sitemap, but now when I generate a sitemap via Keylimetime, the "(high)" text is added to some URLs.

Valid values are 0.1, 0.2, ..., 0.9, and 1.0
Text is not allowed. We tried doing exactly what you said and we're not getting the "(high)" text in our sitemaps.
What version are you running? It probably doesn't matter since this area of the software has never changed.