It has happened to me a few times now, but flipping to nav (or transactions) panel and back quickly fixes it.
Yep.
There are two common causes for this.
Firstly, your sensors got shot-up in combat, in which case you need to reboot/repair to get them working again so you can request docking.
Secondly, a bug that prevents scrolling through the list of contacts, in which case tabbing through the different HUD panels will usually fix it.
Another, less common, possibility is that sometimes, rarely, the HUDs will just be completely empty.
If that was the case, though, the complaint would probably be "My HUDs are empty!!!" rather than not being able to dock.