NOTE: Check your ‘Enforce Mileage In’ setting; Setup, Shop Data, Screen View tab. There is a checkbox for Enforce Mileage In; if set to Yes, change it to No temporarily to complete the corrections work.
Best practice is to:
1. Identify the invoice where the mileage error first occurred, un-post it, correct it and then re-post it with no other changes.
2. Then work your forward, correcting and re-posting other invoices until caught up.
3. Go back to Enforce Mileage In and enable it once again if it applies to you.
TIP: The point of enforcing the mileage input is to provide accurate service history to market with.