I sometimes get the following error when creating a subscription:
Insufficient tokens for quota \'administrator\' and limit \'CLIENT_PROJECT-100s\' of ser
I was hitting a similar error.
I checked the quota section — as per Kamal Aboul-Hosn's suggestion — however it was already maxed out.
A work around was to put a sleep function in the code so the API wouldn't get hammered over a hundred second period. I hope that helps.