CentOS 6.3 server is based on RHEL6 and the vmware convertor 5.0.1 is not supported for the version,
https://www.vmware.com/support/converter/doc/conv_sa_501_rel_notes.html#guestos
Supported Guest Operating Systems
Converter Standalone 5.0.1 supports the following guest operating systems:
- Windows XP Professional SP3 (32-bit and 64-bit)
- Windows Server 2003 SP2, R2 (32-bit and 64-bit)
- Windows Vista SP2 (32-bit and 64-bit)
- Windows Server 2008 SP2 (32-bit and 64-bit)
- Windows Server 2008 R2 (64-bit)
- Windows 7 (32-bit and 64-bit)
- Red Hat Enterprise Linux 2.x (32-bit and 64-bit)
- Red Hat Enterprise Linux 3.x (32-bit and 64-bit)
- Red Hat Enterprise Linux 4.x (32-bit and 64-bit)
- Red Hat Enterprise Linux 5.x (32-bit and 64-bit)
- SUSE Linux Enterprise Server 8.x (32-bit and 64-bit)
- SUSE Linux Enterprise Server 9.x (32-bit and 64-bit)
- SUSE Linux Enterprise Server 10.x (32-bit and 64-bit)
- SUSE Linux Enterprise Server 11.x (32-bit and 64-bit)
- Ubuntu 8.x (32-bit and 64-bit)
- Ubuntu 9.x (32-bit and 64-bit)
- Ubuntu 10.x (32-bit and 64-bit)