As have already mentioned, usually, the problem of snapshot removal isn’t related to Veeam side, but to VMware, instead.
So, as the first step you can follow the manual procedure described above and see whether you experience similar issue or not.
There is also an existing thread at Veeam Community Forum; might be worth reviewing: http://forums.veeam.com/viewtopic.php?f=24&t=2716&p=79491
Thanks.