if SR1V:WEL = 0 then program and erase operations will not be started. WEL needs to be 1 for the erase to work.
If you have sent a Write Enable command before but WEL was still 0 after that, then this might have various causes.
One would be that the device was still busy with some other operation when you sent the Write Enable command.
Another possibility would be a general I/O problem or a misconfigured device (e.g. if QPI is set).
Can you share your complete device configuration, i.e. all register values?
What frequency are you running at? What address do you try to erase (256-Mbit devices require 4-byte addressing!)?
Did you program the location within the same environment? And did the Write Enable command work at that time?