Fallback Code Page &1 not allowed.

What causes this issue?

You tried to change the "Fallback Codepage" but the system did not
accept your choice.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

A code page used for the Unicode conversion has to comply the following
rules:
It must be included in the SAP code page catatog (table TCP00)
It must be round-trip compatible (use report RSCP0125 to check a code
page for its round-trip compatibility)
The code pages 6100, 6200, 6300, 6500 must no be used
For Single Code Page Systems using code page 1100: the code page 1100
can be replaced only with code page 1160
For Single Code Page Systems using code page 6300: the code page has to
be replaced with code page 6301

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.