Discovering a computer in RUM, discovery fails with: "Agent returned error during Discovery" (4351558)

When performing the Discovery and pre-installing agents some of the computers fail with:
"Agent returned error during discovery: More data is available."
 

An incorrect registry entry is causing this error. During the discovery, amongst all other tasks and steps, the tool reads the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UpgradeCodes
UpgradeCode is always a GUID.

But in this case the affected workstations have an entry where the GUID has a space added:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UpgradeCodes\7F1C556234BFA8AE6436BAF3D794CA38 ]

All affected computers have the same GUID with the added space.
Those computers have a particular software installed and this 3rd party application (or add-in) is adding this bad entry into the registry.

RUM has been designed to request the GUID, but it requests that the returned value is 32 symbols (16 byte), and in this case RUM is getting a reply that the value is bigger that 32 characters, hence the error (More data is available) and the failure.
The error can be translated as: There is more data available as requested.

Process those computers without discovering them first. Computers can be processed without discovery and pre-installing agents, once the job is configured and started the agents will be deployed automatically and computers will be successfully processed.