OK, on Sunday, I was doing 2 quests in the Eridan Belt. This was my first time there. Then the servers crashed. When I came back, one of the 2 quests was no longer in my log. I was doing Explore the Eridan Belt, that appear the the exploration section of the In Progress missions. Now, I remember that a quest related to the Romulan Front was also in the Eridan Belt also. But I'm not certain that it was not the same or maybe I had completed it without having to report just by getting there. It don't appear in the Available missions neither. I want to be sure that I don't have the Romulan Front blocked because I lost a quest. I logged a ticket but didn't received an answer yet, so I hope that someone can help me here.
There is no way anyone can block themselves from being able to access an entire Front (Episode).
Besides that the Explore missions are seperate and apart from having anything to do with the Front Episodes and frankly they are some of the least worthwhile missions you can waste your time on.
Its fun maybe to do them for awhile, but eventually you will probably grow to despise the exploration missions and avoid them like they were a plague simply because all of them are pretty much the same no matter where you go.
The only possble exception would be the explore missions in the B"Tran Cluster when you find a fleet action space combat type explore mission when you reach level 50 (Vice Admiral) the enemy ships are high enough level to sometimes give you a decent drop, Even then its nothing to compare to the drops in the STF's. On the upside though B"Tran at least has some pretty worthwhile Data Samples.
The only thing that blocks an Episode/Front is not having completed all the missions in the episode before it. Even then you can choose to simply skip every mission in a particular episode to jump to the next one.