yep, i have problems initiating conversations, but when i'm spoken to i can keep the conversation going most of the times. Guess i don't have the guts to just open my mouth and say whatever crap comes to my mind...
If I've got a goal in mind. I won't have problems speaking to other people...
Like at the beginning of university. I found myself just randomly speaking to people with the intention of meeting new people and finding out about them.
Having to speak to them now when topics have run dry, basically requiring me to think of things to say... now that's the major problem. I usually end up staying silence or chip in a comment if I think the other people are becoming uncomfortable.