Backup failed with error 1859

Hi,

since 2 Days my Backup failed 

i get the Error

Error: 1859 - [rofs_cant_write_detail] RDA can't write //vRanger_423261c9-3f10-7d91-3c8f-8a1dae2c2d64/vRanger_20210510_093916_44b4de82-3e41-4984-ac6c-64fa904c1e0a/.b88adee5-33ec-4bfe-8e28-736dc4a38961/.b88adee5-33ec-4bfe-8e28-736dc4a38961.var (Service is down)

backupdrive is an QUEST DR4100 with RDA