we have 2003 enterprise edition x86(failed), 2003 standard x64 edition(success), server 2008 r2 standard(success), server 2012 r2 standard(success)
i've go through the documentation and in section "hyper-v integration services required in the Vm", no Win Server 2003 was mentioned.
the backup failed with the following error:
01/20/2016 09:09:54 - Info bpbrm (pid=143593) reading file list for client
01/20/2016 09:09:54 - Info bpbrm (pid=143593) start bpfis on client
01/20/2016 09:09:54 - Info bpbrm (pid=143593) Starting create snapshot processing
01/20/2016 09:09:55 - Info bpfis (pid=5792) Backup started
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - vfm_freeze_commit: method: Hyper-V_v2, type: FIM, function: Hyper-V_v2_make
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - snapshot services: snapshot creation failed: unknown error.
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - vfm_freeze_commit: method: Hyper-V_v2, type: FIM, function: Hyper-V_v2_make
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - snapshot services: snapshot creation failed: unknown error.
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - snapshot processing failed, status 156
01/20/2016 09:10:47 - Critical bpbrm (pid=143593) from client BELVLL21: FTL - snapshot creation failed, status 156
01/20/2016 09:10:48 - Warning bpbrm (pid=143593) from client BELVLL21: WRN - ALL_LOCAL_DRIVES is not frozen
01/20/2016 09:10:48 - Info bpfis (pid=5792) done. status: 156