A Veeam proxy server is configured as follows.

Given the provided transport modes and the fact that no modifications are allowed to these settings, a possible cause for the restore of a VMware virtual disk to fail using this proxy server is C: The virtual disk is thin-provisioned. In the transport modes shown, the Direct storage access and Virtual appliance options would require the VM disk files to be accessible in a certain way that might not be compatible with thin-provisioned disks depending on the storage configuration and the current state of the VM. If the storage integration specifics or the snapshot handling do not support the thin-provisioned format, the restore operation could fail. It's important to ensure that the transport mode selected is compatible with the type of virtual disk being restored to prevent such issues.