Before attempting to withdraw the cobblestone

After

Correction: this happens with numbers 56 and above

Your network doesn't have enough power, add some regular or Dense Energy Cells.

Oof

as a side note, there's a quest specifically on this topic in the quest book called "Oops... A Blackout!". This is a common occurrence for players when channels are disabled in AE2, as the network doesn't have as much power buffering as it usually does from the ME Controller.