Wrong Retail release (at least 1.2B required)

What causes this issue?

The system on which the upgrade is running has a wrong Retail release
level. It is either too early (at least 1.2B is required for the
upgrade) or is the same as or higher than 4.0.

System Response

No conversion carried out.

How to fix this error?

If your system has a Retail release level < 1.2B, you must upgrade to
this release.
If your system has a (standard) release >= 4.0, conversion is not
necessary.

Error message extract from SAP system. Copyright SAP SE.