This error message is outputted, because you select /translation for CDS feature by dialog of [Select Qualifier] button.
Generally, since /translation qualifier is automatically created according to items under CDS feature, do not enter any amino acid sequence.
So, you can fix the error by removing /translation qualifier.

For your information, /translation qualifier is required only in case describing with /exception qualifier.
Typically, /exception qualifier indicates “RNA editing” is occurred on mRNA. In that case, conceptual amino acid translation of genome sequence is different from protein product of real mRNA molecules.

Example of Submission: B09) RNA editing
How can I input amino acid sequence (/translation qualifier) for CDS feature?
How to confirm translated amino acid sequences (i.e. /translation qualifier) for CDS features?
The amino acid sequence in the value of /translation qualifier seems to be incorrect.