Activesync devices list is empty in EMC and console

Hello to all

Two users avec issues with ActiveSync and iPhone.

Using the same configuration, their iPhone first connect to exchange 2010 but never sync mails.

In EMC when I try to remove the activesync device, the list is empty.

With the console: # get-ActiveSyncDevice -MailBox "<my MB>", the instruction return nothing.

How can I reset a device I cant' see ?

Thanks for your help.