Invalid time passed (&)

What causes this issue?

The time must be transmitted in the format "HHMMSS" and is then checked
by the system with respect to its validity.

System Response

Conversion is not possible.

How to fix this error?

Correct the application program, in particular by entering the time in
a suitable field. This way the system performs an automatic check.

Error message extract from SAP system. Copyright SAP SE.