This has happened to me in the past and, in fact, had the issue for the last couple of weeks. Then a few days ago, it cleared up.

I had this discussion awhile back with other users and it is my understanding that it isn't AW2000, it is an ebay issue. Not sure, however, what causes it.

This link doesn't solve the problem but gives a "sort of" explanation of what is happening with it.

https://forums.developer.ebay.com/questions/540/serious-error-518-call-usage-limit-has-been-reache.html

My experience is that about 7-8 p.m. PDT it start but ends at midnight.