Is there a trick to connecting an optical cable?

I'm getting (supposedly...) the new DirecTV HD DVR installed today. It uses optical for the DD connection. I was using digital coax before.
I can't figure out how to connect the optical cable to the video 1 optical port on the 990.
I seems there's a little plastic "door" that folds down, out of the way, as I try and insert the optical connector. But, the cord connector tip won't go in all the way and seat. I've rotated the connector end it thru all 4 quadrants and am certain I've aligned it so the fat side and skinny sides of the connector are correctly oriented with the port on the 990.
What am I doing wrong? Am I supposed to somehow remove this "fold down", dust-cover door?
Thanks

Was there a cover on the end of the optical cable and if so did you remove it?

You shouldn't have to remove the"dust door".

Well, it turns out the optical cable I bought has these little plactic dust covers on the tip of the cable. Once I removed it, it connected fine. Problem solved.
So, I spent an hour on the phone with DirecTV, getting handed off to different people, finally getting someone to give me the phone number of the local installed they contracted with to deliver/install my equipment today. So, I call them and find out that they won't be here from 8-12 as I was told by DirecTV, but rather between 3 and 4 p.m. Nice of them to give me a courtesy call. NOT.
I've moved into a new house, and am setting up my system in the upstairs "bonus room" to make it my new HT room. It's a bigger room than the one I had at the house I was previously in. The only thing I've noticed is that I'm getting some bleed-thru from a local radio station (there are 3 or 4 TV/radio twrs all within a mile or two of my house). I can hear some radio station very faintly in my right side surround speaker. It doesn't seems to come thru the other 6 spkrs (nor the sub). Weird, because the right SS sprk cable runs right along the right rear surround cable, and that one doesn't get any interference. Any suggestions for this issue?

Thks mzpro. I must have been writting my post when you were posting yours.
Anyone know of some device or technique to deal with RF energy entering my spkr cable? It seems by repositioning it, it has attenuated somewhat. But, the position that helped has it drawn out from along the baseboard into the room. Not an attractive solution.

with 2 conducter speaker cable with shield, you wire up the shield to ground only at one end.