If you try to start a VM in XenSource and you see an error that SR_BACKEND_FAILURE_46 then one way to resolve is to detach the storage and reattach while forgetting and resetting the VM’s uuid. To do so, first locate the VM in question and go to the Storage tab to find the SR.
Click Properties and add _temp to the end of the name so that you can easily find it to reattach. Then click on the Detach button for the storage. From the Console for the host, run the following (assuming the VM is called JACKED):
xe vdi-list name-label= “JACKED_temp”
Note the VDI UUID and SR UUID, which we’ll call $VDI_UUID and $SR_UUID respectively. THen run these commands:
xe vdi-forget uuid=$VDI_UUID
xe sr-scan uuid=$SR_UUID
xe vdi-param-set name-label=JACKED uuid=$VDI_UUID
Open XenCenter and go to the VM > Storage tab and click Attach. Choose JACKED_temp and then click Attach Disk. Finally, choose the VDI that you were working on and click Start. The VM should fire up now. Good luck!