Whenever bpbrm says "Error from client" check the client log.
In this case, the important client logs are bpfis and bpcd. Also check the bprd log on the server. For the client logs, set the logging level in two places. Set it to 3 in the main Logging screen, and to 2 in the Windows Client, Client Settings screen. For bprd, set the logging level for the master server.
The "state files" are the snapshot state files and the Exchange metadata files that bpfis produces while making and processing the snapshot. NetBackup uploads the files from the client NetBackup\online_util\fi_cntl folder to the master server's client database. This is in case your client melts down, or you want to redirect the restore to another client.
The state files on the master server are in a flat-file folder under NetBackup\db. The transfer process is as follows:
1. Request from bpfis to bprd to make the transfer.
2. Bprd request to bpcd to read the files.
3. Bprd writing the files.