Upgrading VMware vCenter from 5.5 to 6.0 you may get and error in the pre checks:
SSL3_GET_RECORD:wrong version number' while validating ssl certificate.....
The reason we were seeing the SSL3 error was due to the fact that SSL v3 is disabled by default in vCenter Server 5.5 U3b. The install was still trying to communicate to the STS and Identity Management services through SSL v3 which caused the failure.
The workaround for this was to enable SSL v3 again in vCenter which allowed the upgrade to proceed.
The steps to perform this are as follows:
1. Open file C:\ProgramData\VMware\CIS\runtime\VMwareSTS\Conf\Server.xml
2. Remove the tag 'sslEnabledProtocols="TLSv1,TLSv1.1,TLSv1.2' from the following line in the server.xml file
3. Restart VMwareSTS and VMwareIdentityMgmtService services.
4. Reattempt the upgrade to 6.0