Conflict between maping drives and backup software in Windows Server 2003

Hello: I’m having trouble with some shared and mapped folders in a local network (also with a domain) every time I run a backup with any backup software, first when I’m running the full backup the software (I tried with Cobian and Handy Backup) it says that it were unable to reach the source folder and then after that the shared and mapped folders are not accessible in the network, when I go to the network and open the folder it shows nothing inside. All this folder (source) are in an external hard drive I connected to the server through an expansion card PCI to USB 3.0
Does anybody have any suggestion, please???
Thanks