Friend, new to SE, contributing to WebApps just sent me a screenshot, that shows, that reputation updates are reflected on general counter (user bar at top) but not in comments mechanism:
Is this a bug or something, that is wanted / required?
EDIT: This is of course temporal. After refreshing the page, limitations to writing comments were removed and comment could be written.
The decision whether this error is rendered is made on the server when the add comment link is rendered (it has an additional data-reg="true" attribute), since it also depends on other things that would require an additional round-trip to the server each time a user clicks this button - which we don't want.
After you've reached the required rep you need to refresh the page (so it's rendered again) to be able to add comments.
