Found another quest that I can't complete; this time it's in the Liberation of Skyrim quests.

After killing off the garrison at Fort Snowhawk, I return to Galmar at the Stormcloak encampment. I recieve 800 gold for completing that assignment, and then it updates for the attack on Solitude; however, even though it tells me to report to Ulfric for orders, the quest marker stays on Galmar, who I can't talk to (no dialogue options, he just keeps repeating for me to join the men for the attack). When I go to talk with Ulfric, there's no option for receiving new orders from him. And I cannot enter Solitude, since it's already started the attack (but nobody shows up for it, no troops to meet, no defenders, no one).

This is the second quest that I cannot complete because of a glitch. Going back to a previous save doesn't help as the same thing happens again.