The full error is:
InvalidArgumentException: <RC=0xCB[LCB_ERR_INVALID_ARGUMENT (203)], There was a problem scheduling your request, or determining the appropriate server or vBucket for the key(s) requested. This may also be a bug in the SDK if there are no network issues, C Source=(src/store.c,288)>
In the Name of collection field, enter a name for the collection. A collection name can only contain the A-Z, a-z, and 0-9 characters as well as the -, _, and % symbols. It cannot start with either the _ or % symbols. It cannot be longer than 251 characters in length and is case-sensitive.