This occurs on some boards and its cause can be somewhat elusive. The W25X20CL is a memory chip on the Einsy Rambo board. It is an issue when flashing the firmware and is normally caused by the following:
A poor connection to the LCD module or a faulty LCD module can generate issues when flashing the firmware.
Try to flash the firmware again with the LCD module disconnected or its cables re-seated.
Contact your developers of the firmware and check if anyone else has had the issue. We, unfortunately, can not provide support for custom firmware and modifications.
With more and more languages being supported in the Firmware, some older boards do not have the capacity to store all the languages included. You can get this error on the Einsy Rambo rev.10.a without a daughter-board plugged into the LCD ports. In this case, you will still be able to use the firmware fully but only with English language. The daughterboard is no longer offered, therefore if the board itself is found to be the problem, it needs to be replaced.
Like all electronics, it can fail, so if the points above do not provide any insight into your issue, please contact customer support to resolve it.