I need to chime in here as well.
Using 1.6.6.
Made a few Mod-Archives from a JSGME-type folder structure with the built in tool. I enter a version number, 1.0.0 if the author has none set or the real version number if there is one, and a brief multi-line description. Creating the Mod-Archive goes without a hitch and it's showing fine in the mod list.
When I then try to create the xml, also using the built-in tool, I get no errors. I save the xml as is, no input or editing what so ever (except pasing my base url) and upload it to my server.
When querying the repo I get the same error as reported above on some of the mods' descriptions and on some not and I see no to my eyes apparent error in the xml. If I edit the xml and remove all description lines except the first on the two descriptions causing the error, the error disappears. No matter what the lines after the first one contains an error is produced when querying the repo.
In my case, it's the description from the mods "ENV Highways Villages Mod" and "ENV Starways Black Sea map 2.5" that makes OvGME unhappy. Check the differences on the two xml's below.
http://repo.jtf16.org/DCS_Bamse/repo.xml
http://repo.jtf16.org/DCS_Bamse/repo_with_error.xml
The repo is on a server atm running Win2012R2 with HFS2.3i, but tested with IIS 8 and on a separate webserver running ubuntu/apache 2.2. Error still shows.
Please note that this is a test/wip-repo and is not meant for public use in any form.
My workaround is to keep the descriptions for these two mods as a one-liner for now.
All editing is done from within OvGME, no external tools except FileZilla Client for uploading stuff to my web server.
Part 2.
Second error is probably is unrelated, but when downloading from the working repo above, the download for the ~2.5GB big texture pack made by Starways (ENV Starways Black Sea map 2.5.zip), the download never completes no matter how many times I try to re-download with OvGME. Downloading the file with IE, Chrome or FF using the same exact url from inside the xml works fine first try.
Part 3.
OvGME rocks. I'm very new in the DCS world but I'm a regular Arma3 player where centralized repos for private servers is a very common occurrence to make sure everyone is running the same content at a certain given point in time. I've been missing this for DCS and totally missed this thread until a few days ago. You, sir, have my axe, sword and whatever else might be necessary. Good job!