Failed: [path to disk].vmdk cannot be downloaded, 'HTTP/1.1 500 Internal Server Error'

Problem

Error during Backup:
Failed: [path to disk].vmdk cannot be downloaded, 'HTTP/1.1 500 Internal Server Error'.

Log file:
[3608] 21.09.2015 00:51:19 [3663887] Trying to download using webservice
[3608] 21.09.2015 00:51:19 [3663887] Running Download on ESXi WS: xxx.vmdk (bytes: 42949672960, start pos: 0)
[3608] 21.09.2015 01:06:50 [ERROR] HTTPS re-connect to <IP>(Done: 7992625608/42949672960): null
[3608] 21.09.2015 01:06:56 [ERROR] HTTPS re-connect to <IP>(one: 7992625608/42949672960): null
[3608] 21.09.2015 01:07:01 [ERROR] HTTPS re-connect to <IP>(Done: 7992625608/42949672960): null
[3608] 21.09.2015 01:07:01 [ERROR] Download Error: xxx/xxx-flat.vmdk cannot be downloaded, 'HTTP/1.1 500 Internal Server Error'
[3608] 21.09.2015 01:07:02 [ERROR] [3663887] File transfer error. xxx/xxx-flat.vmdk cannot be downloaded, 'HTTP/1.1 500 Internal Server Error'

Cause

This problem is caused by an ESXi WebService connection lost during the files transfer.

Since the problem is outside VM Explorer it cannot be solved by HPE.

Fix

Enable the VM Explorer Agent for the affected hypervisor to change the transport method

Edit Server -> SSH / VM Explorer Agent -> Try to use VM Explorer Agent on ESXi