The system is setup to block anything which seems suspicous from new users which fits the pattern of scammers or spammers.
For example,
- less than a certain number of posts, and posts or conversation messages have web page links.
- several conversation messages without posting in the forums, a classic pattern of forum and craigslist ad scammers, etc.
I'm not saying that's you, but the system doesn't know the difference - and it's designed for people here to be part of the community, not for people here solely to buy or sell.