Some builds of the OpenSSL binary shipped in early versions of the (c)ESXi 6 branch can't decode base64 strings which may lead to (c)XSIBackup failing at the time to run some commands.
You can reproduce the error by running this code snippet
echo 'Uj0iJCggKCIvc2NyYXRjaC9YU0kvWFNJQmFja3VwLURDL3hzaWJhY2t1cCIgLS1mcmVlLXNwYWNlICIvdm1mcy92b2x1bWVzL2RhdGFzdG9yZTEvcmVwbGljYXMvMyIpIDI+JjEgKSI7ZWNobyAtbiAkPyI7IiRSCg==' | openssl base64 -d
It should return
R="$( ("/scratch/XSI/XSIBackup-DC/xsibackup" --free-space "/vmfs/volumes/datastore1/replicas/3") 2>&1 )";echo -n $?";"$R
In case your OpenSSL binary is affected you would get nothing.
You can ignore the additional bug that causes the constant output:
WARNING: can't open config file: /usr/ssl/openssl.cnf
We have already addressed it by filtering it out.
We'll try to address this issue by working it around.