Ah, the age-old question: "How come my press pass didn't work?"
Sorry to hear about your experience. As a working photojournalist, I can tell you that yours is not unique. Here in the U.S. press access is determined by a number of factors the first being what event you are trying to cover.
As stated above, campaign coverage with open press is usually easy to gain access to. At an event with President Obama last month though I witnessed quite a few journalists being turned away at the door after not getting pre-registration taken care of in advance.
The best thing to do before going to an event (with adequate credentials) is to contact the event organizers before and inquire about what credentials you will need. It's pretty easy as most major events have a press kit or contact that is released before the fact. Tell them who you are working for and what you will need and they are usually pretty cool with helping you out. I always ask for a contact name (and possibly cell phone if I can get one) before so if I hit a snag when I arrive I have a name to drop or a cell phone I can call.
If all else fails, just turn on the charm.
"Oh, you're kidding me! I didn't realize that there was a pre-registration for this event. Do you think there is someone I can talk to about getting inside? My editors are not going to be happy with me at all if I don't get some good photos from your event today."
That, believe it or not, is a surprisingly effective route that works more often than not. I also try this one if the person manning the entrance seems to be cool or a volunteer who might not care or know better.
"Come on buddy. Can't I just get in for 30 minutes? I won't get in the way and just need to get a photo or two before I get out of here."
Finally, if all of the above fail, I always carry $100 in cash in my pocket to bribe my way in. My editors always reimburse me for it and have an understanding that it probably wasn't my fault in the first place that we lacked the pre-registration needed to get in. Also, on that note, I found that Rueters and AP shooters often will tell the event organizers that you're with them if you slip them the cash instead of the security guy.
If all else fails, do what you did. Just get photos from the best place possible.
Bottom line: When at first you don't succeed, try and try again. It's amazing the access you can gain when you don't take "No" for the answer right off the bat.
