Error during backups of VM

Hello,

I have a problem during backups of VM. All my backups end with error 4239. More exactly, the description is "Unable to find the virtual machine", the snapshot fail and there is no backup.

I have two vSphere account with enough permissions, with one I have this error, and with the other one I have an error 6, the snapshot is OK but the backup fail.

I've configured vxms, and here is the log.

I don't understand why I have this error. I think I have the right permissions, and communications between ESX and Master/media are OK.

My Master server and Media server are 7.6.0.3, my vSphere is in 4.1 and my OS is Windows 2008R2