Environment
- vBackup running 32-bit client
- VDDK 5.1 installed
- Backups written to external USB 2.0 HDD
- host server running ESXi 5.5
- thick provisioned virtual disks on the host server

Consistent backup error in vBackup 4.0
[NFC ERROR] NfcNetTcpRead: bRead: -1
[NFC ERROR] NfcNet_Recv: requested 261704, recevied only 180224 bytes
[NFC ERROR] NfcFile_RecvMessage: data recv failed. retval = 3, expected 261704
[NFC ERROR] NFC_NETWORK_ERROR
Failed to convert disk: Operation completes asynchronously (0x300004650).

Backup Scenarios
1. vBackup settings: License=Advanced, Compression=Basic, backup written to external USB 2.0 HDD
-> backups complete successfully

2. vBackup settings: License=Standard, Compression=None (only option available), backup written to external USB 2.0 HDD
-> backups failed

3. vBackup settings: License=Standard, Compression=None (only option available), backup written to local folder on HDD where vBackup/VDDK installed
-> backups complete successfully

4. vBackup settings: License=Standard, Compression=None (only option available), backup written to network share
-> backups failed

Issue appears directly related to VDDK failing to write non-compressed backups to remote locations
Only solutions appears to be use of high performance target location (USB 3.0?) and/or use of compression

[NFC ERROR] NfcNetTcpRead: bRead: -1
[NFC ERROR] NfcNet_Recv: requested 261656, recevied only 16384 bytes
[NFC ERROR] NfcFile_RecvMessage: data recv failed. retval = 3, expected 261656
[NFC ERROR] NFC_NETWORK_ERROR
Failed to convert disk: Operation completes asynchronously (0x300004650).

This error is reported by VMware Virtual Disk Manager. This error happens when the connection to the host server times out between data reads. VMware Virtual Disk Manager copies data from the host server to the backup target in "chunks". VMware Virtual Disk Manager makes a request to the host server for a chunk of data, writes it to the backup target and then goes back to the host server to request another chunk. If the write operation takes longer than the connection timeout allows the host server will deny the next request and VMware Virtual Disk Manager will exit with this "NFC read" error.

This error is most often seen with the following scenarios:

1) Source VM's disks are thick provisioned and the compression level setting of the backup job is set to "None"

2) Target storage is slow or performance is degraded

3) Target storage is beginning to fail

4) On rare occasion we have seen this error when the VMFS (host) storage is beginning to fail

Hopefully this helps you troubleshoot. Start with the simple stuff as it looks like you are doing (by trying a backup to local storage). You might try restarting the backup server and disabling antivirus software on backup server or excluding the folders backups are saved in.

Please let us know what you find out.

PS All my VM backup jobs are set to use Basic compression