Yes, there are some restrictions on number of posts you can contribute. They are imposed to make sure that spamming the site with a heavy messaging is avoided.
A few restrictions include the following -
1. You can not create more than 10 threads per day in the forum section. If you exceed the limit, you will face automatic ban from creating new threads for five days.
2. If you have more than five deleted responses in Ask Experts section in last five days, you will get restricted access for the next five days.
3. If more than five of your articles are pending for review or have been sent by editors to pending section for want of correction, you will not have be allowed to post any new articles till those are reviewed.
4. Though I am not sure, but if certain number of your ASK Expert section responses are pending for review, you will not be able to post new responses until a couple of them are reviewed.
There is no restriction, however on posting responses in the forum.
Live....and Let Live!