MyCloudEX4100 & TimeMachine Issues

Probably not the first user with this problem, but i couldn’t find a solution so i give it a shot over here.
I’ve got a MyCloudEX4100 with Firmware 5.22.113.
Sharing works fine, i could copy lots of data to the desired designations.
But then comes TimeMachine.
I can see the TimeMachine share in macos (12.4). When i click on the folder in the finder a window is opening but changing instantly to an error message that the folder can’t be found.
Once i managed to make a complete TimeMachine backup - but when i try to make another backup the volume can’t be found.
When I try to setup TimeMachine on my MacBook it is not possible, as the guest credentials are not acceptet. On my main Mac I also used the guest credentials for the initial backup - but a second one is not possible.
Constantly i get this error message on the MyCloud device:
CIFS: Authentication for user [GUEST] has FAILED.

Only one user (me) tries do do stuff with the MyCloud device and the EX4100 is notconfigured to be used outside of the home network.

Does anyone got an idea on how to get rid of this behaviour in order to be able to use the EX4100 as a TimeMachine target?

Hi @uselessuser,

Please refer to the article My Cloud: CIFS Authentication For User Nobody has Failed:

If further assistance is needed, please open a case with our support team at the following:

Sorry, but I can’t see how the linked article could help as I am using macos.

The by @Keerti_01 provided solution is worthless, as the error is a result of a major firmware bug.
It has already been discribed months ago i.e. in this thread:

I could do backups from all machines without any changes to my Macs, router or other equipment - only by setting the quota for time machine to 100%.

This is a major firmware bug.
WD is selling devices to customers where essential features are broken by a firmware update.

Not only, also several issues found.
This major bug was observed in several versions before too. The issue related to size limit - I didn’t checked protocol by sniffer but seems this is issue from size limit reported not correctly.

afp protocol was WA for backups but WD has no longer support it. It looks like somehow WD shoots himself in the foot.

It seems like this behaviour of the MyCloud series is not a bug.
Instead it is a documented feature that you can only use TimeMachine when you use 100% of the size of the volume.

MY Cloud OS 5 Time Machine Backup Settings.

  • Ensure Apple Time Machine backups are configured to use the My Cloud TimeMachineBackup share.
  • Ensure the My Cloud TimeMachineBackup share has the “Mobile & Web Cloud Access” set to OFF at the Share level.
  • Ensure the Time Machine Backup Maximum Size is set to the default of 100%.

It is written (o better hidden?) in this support document.

This simply means for macos users that they can use the device, when they want to use it for TimeMachine, ONLY for TimeMachine.