Based on what you emailed me:
Where you have this:
<Starting_Forces> Yevetha, Polneye, Yevetha_Star_Destroyer_Two </Starting_Forces>
<!-- Polneye
<Starting_Forces>Yevetha, Polneye, Y_Ground_Barracks</Starting_Forces>
<Starting_Forces> Yevetha, Polneye, Yevetha_Infantry_Squad </Starting_Forces>
<Starting_Forces> Yevetha, Polneye, Yevethan_Heavy_Scout_Squad </Starting_Forces>
<!-- Jtptan Space Forces -->
<Starting_Forces> Yevetha, Jtptan, Y_Star_Base_1 </Starting_Forces>
You have a comment starting at Polneye and going all the way until the "-->" after Jtptan. Basically everything between <!-- before Polney and --> after Jtptan are ignored by the game (shown in my post by the fancy green colouring). Usually this just means it'll load fine and just ignore that data, but you get a syntax error because there's an additional "<!--" inside the comment, so it's essentially trying to put a comment inside a comment, which isn't going to work. If anyone says "commentception", I will ban them for a week.
All you need to do is change the above to this:
<Starting_Forces> Yevetha, Polneye, Yevetha_Star_Destroyer_Two </Starting_Forces>
<!-- Polneye-->
<Starting_Forces> Yevetha, Polneye, Y_Ground_Barracks</Starting_Forces>
<Starting_Forces> Yevetha, Polneye, Yevetha_Infantry_Squad </Starting_Forces>
<Starting_Forces> Yevetha, Polneye, Yevethan_Heavy_Scout_Squad </Starting_Forces>
<!-- Jtptan Space Forces -->
<Starting_Forces> Yevetha, Jtptan, Y_Star_Base_1 </Starting_Forces>
Also, every GC has a code section for each GC. Right now you have them added in the Imperial version, there's other sections for the NR, EotH and PA, indicated lower in the file by
<Campaign Name="Sandbox_All_Rebel">
etc