I just starting having this exact same issue this morning. One particular member was able to comment at 12:06 p.m. and then at 12:12 p.m. began getting the message “Unable to receive your comment at this time.” Other members, in the same member group have been able to comment since. I logged in as ten different members in that group and got the error message eight times, and could only successfully submit a comment twice. I have had no issue logged in as a Super Admin, but in a third member group, none of the five members in that group could submit a comment.
Until today, none of my members have had any issue submitting comments.
Additionally, this doesn’t affect the ability to post weblog entries for those five members in that ‘third group’, nor does it affect any members ability to post in the Discussion Forums.
I’m on EE 1.6.9 Build 20100430.