Thanks for joining this thread, @M Simon. 

I'm here to share some details about accessing QuickBooks for Windows on a Mac computer. Aside from checking the integrity of the file, we can edit the length of entries in the memo field. Here's how: 

1. Open the company file in QuickBooks for Mac.
2. Generate a Transaction detail by Date report for all dates:
3. Go to Reports, then select Transaction detail by Date.
4. From the Dates drop-down, choose All Dates.
5. Review the Memo column (the Item Description field on forms) for any text longer than the maximum 100 characters.
6. Double-click the transactions with large memos or descriptions, then either delete or shorten those memos to less than 99 characters.
7. Create a new backup file for your QuickBooks for Windows file, then do the conversion again. Also, you may utilize this resource for your reference: Convert a QuickBooks for Mac file to QuickBooks for Windows.

If the same thing happens, I recommend contacting our QuickBooks Support Team to ensure the setup is correct.

1. Go to this link: Contact Us.
2. Choose QuickBooks Mac Desktop.
3. Click on the Company File menu.
4. Scroll down and click either Get Phone Number. 

You can get additional information about fixing the error after QuickBooks for Mac to Windows company file conversion: Error: QuickBooks is not able to convert your Mac file to a Windows file. 

Should you need any further assistance with converting your file, let me know in the comments section. I'd be happy to help you in any way that I can. Have a great day!