Hello Grace,
As per your note, you have defined your own fiscal year, which is non calendar fiscal year variant Z1. You have not maintained the period control keys for this particular Fiscal Year Variant Z1 and hence, you are receiving the above error message.
You need to maintain the period control for Fixed Assets in the Business Configuration under the activity Other Fiscal Year.
1. Open the activity Other Fiscal Year.
2. Click on open and select your fiscal year variant.
3. Select subtab Period Control for Fixed Assets under the Fiscal Year Variant Details.
4. Maintain settings for your current fiscal year and try to do the migration.
Hope this information will help you.
Regards,
Annapurna