Entry & not allowed with this G/L account

What causes this issue?

The field selection for the G/L account does not allow input in field
&V1&.

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?

Do not enter any data in this field, or
Check field selection for the G/L account, or
Enter a different G/L account.

Error message extract from SAP system. Copyright SAP SE.