Hi Karim,
Error 208 is a common error so we need more information.
Please following the instruction in following article:
Error ID: 208
https://technet.microsoft.com/en-us/library/ff399219.aspx
If synchronization has not occurred since the last recovery point was created, you can synchronize the replica with the protected data on the protected computer and then create a recovery point.
And:
How to Synchronize a Replica
https://technet.microsoft.com/en-us/library/ff399458.aspx
To manually synchronize a replica
1.In DPM Administrator Console, click Protection on the navigation bar.
2.In the display pane, select the replica that you want to synchronize.
3.In the Actions pane, click Create recovery point - disk.
4.In the Create Recovery Point dialog box, select either Create a recovery point after synchronizing or Only synchronize. If you select Only synchronize, changes since the last synchronization are transferred and applied to the replica.
5.Click OK.