This was a very common problem last year, and all I got were various excuses. After eCogra got involved it turned out that it was the casino not having the funds in their own Neteller account at the time they initiated the transaction. This was made worse by the fact they did not have any monitoring in place to catch this problem, and it just went unresolved until I complained to the casino.
To date, I have never been told WHY this just happened again and again over the space of many months, with no-one bothering to make the necessary changes to put a permanent fix in place.
Recently, this has happened much more rarely, and I hope this means that changes are now in place.
I found Neteller just as useless as the casino, especially since at no time did they spot the "bleedin' obvious", that the sending account was empty, and it was Neteller themselves that were denying the credit due to insufficient funds in the sending NETELLER account.
Had Neteller told me this, I could have blown all the casinos Bulls*it out of the water, and told the casino to pull their finger out and stop blaming "lost internet connections" or "Neteller problems".
Since this is an MGV casino, I bet I can tell which one
