Delray Dave said:

My Troops Cannot Upgrade -- on the upgrade screen, the 'UPGRADE' button does not turn green, though I have 3 troops with more than enough experience points to move onto the next level -- my troops cannot be upgraded....

Lord Delray

i guess you are talking about upgrading them with medals.

consider also two point more for them to be able to upgrade. First check if you have discovered the lost art required and you have it at the level you are asked for upgrading and second check if you have medals enough for upgrading

you have to be sure about all the requeriments to be able to upgrade them. if one of them fails you cant upgrade them though u have the xp enough

hope this can clarify ur doubts.