The answer to the second part of the question is a resounding 'no'. If I don't like a pairing (or at the very least be able to see it) then I would never attempt to write it as I know I couldn't do it justice.
There are a few pairings that whilst not being 'my' pairing I believe I would be able to write, because whilst I don't necessarily see the pairing, I can either see how others can see it or it's canon. For example whilst my Buffyverse pairing is Buffy/Angel, I think I would be able to write a Buffy/Spike story and do it reasonable justice. However, I know for a fact I could never write Gibbs/DiNozzo or Fraser/Kowalski as I simply cannot see either pairing.
When I was writing NCIS and I ventured outside of my main pairing and in fact expanded my pairings rather dramatically, I did end up writing pairings I never thought I would, even with characters I didn't necessarily really like; a couple of these pairings I actually 'picked up' via other people's stories - Kort/Jenny was one of those. However, in all of those cases I could see the pairing about whom I wrote, at least at some level.
The answer to the first part of the question is a slightly hesitant 'no' insofar as I do not believe or remember ever trying to write a pairing I liked but not being able to. However, I wouldn't swear under oath it has never happened. I have started stories that have subsequently come to a halt and have been abandoned. However, I really don't think I've ever failed to write a story for a pairing I like.
I have considered writing the odd story for a pairing I like and then decided not to do so. I've maybe even run an idea through in my mind. But that's about all. If I like and see a pairing enough to really want to write them, then I do so. If I don't, I don't.
10 – Pairings – Have you ever gone outside your comfort zone and written a pairing you liked, but found you couldn't write, or a pairing you didn't like, and found you could?
11 – Genre – do you prefer certain genres of fic when you're writing? What kind do you tend to write most?
12 – Have you ever attempted an 'adaptation' fic of a favourite book or movie but set in a different fandom?
13 – Do you prefer canon or fanon when you write? Has writing fanfic for a fandom changed the way you see some or even all of the original source material?
14 – Ratings – how high are you comfortable with going? Have you ever written higher? If you're comfortable with NC-17, have you ever been shocked by finding that the story you're writing is G-rated instead?
15 – Warnings – What do you feel it most important to warn for, and what's the strangest thing you've warned for in a fic?
16 – Summaries – Do you like them or hate them? How do you come up with them, if you use them?
17 – Titles – Are they the bane of your existence, or the easiest part of the fic? Also, if you do chaptered fic, do you give each chapter a title, or not?
18 – Where do you get the most inspiration for your fics (aka 'bunnies') from?
19 – When you have bunnies, do you sit down and start writing right away, or do you write down the idea for further use?
20 – Do you ever get bunnied from other people's stories or art in the same fandom?
21 – Sequels – Have you ever written a sequel to a fic you wrote, and if so, why, and if not, how do you feel about sequels?
22 – Have you ever participated in a fest or a Big Bang? If so, write about your favourite experience in relation to one. If not, are there any you've thought about doing? And if not, why not?
23 – When you post, where do you post to? Just your journal? Just an archive? Your own personal site?
24 – Betaing – How many betas do you like to use to make sure there aren't any major flaws in your fic? Do you have a beta horror story or dream story?
25 – Music – Do you listen to music while you write? Do you make playlists to get into a certain 'mood' to write your fic? Do you need noise in general? Or do you need it completely quiet?
26 – What is the oddest (or funniest) thing you've had to research for a fic?
27 – Where is your favourite place to write, and do you write by hand or on the computer?
28 – Have you ever collaborated with anyone else, whether writing together, or having an artist work on a piece about your fic?
29 – What is your current project or projects?
30 – Do you have a favourite fic you've written? What makes it your favourite? And don't forget to give us a link!