Just checking has this issue been resolved. I am also getting the same error now. I am trying to post for 01 March 2012 and the same error comes up. The period is open with normal code.
Please let me know how did you manage to resolve this issue.
The periods were existing and were already open. We found out that the issue was because of some irrelevant code inserted by the developers which resulted in stopping all furture postings. The issue has now been resolved.