First, check the summary for the operation. Near the bottom, it should provide more information (such as "Must Provide A Primary Resource", or "Insufficient Permissions On Resource"). Usually, this message is self-explanatory.
Must Provide A Primary Resource - You have given no resource name for the operation. Select one using edgemenu:Admin:Set Default Backup Resource (for edgemenu backups), or in the scheduler (for unattended backups).
Resource (resource name) Cannot Be Accessed - You have given a resource name that is not defined. Be sure you have not renamed the resource (or the machine on which it resides!) in the resource manager. Try re-selecting it through edgemenu or the scheduler to be sure the resource has the same name.
Resource Type Must Be A Data-Transfer Resource - You are trying to do a backup to a resource that is not a data transfer device, such as an autochanger. Normally, it is not possible to select such a resource to begin with, but it is possible you have defined a new resource with the same name as the old one.
Insufficient Permissions On Resource (resource name) - You don't have enough permissions to do whatever it is you're trying to do with the resource. For example, most non-root users cannot write to a device node. This error can also indicate that you are backing up to a disk file which does not exist. In this case, simply create a zero-length file with the filename given in the Data Node field of the Resource Manager. NOTE: do this *ONLY* if you are trying to back up to a disk file, *not* to a tape drive or other device!