Thanks for coming into the Community forum, @Areaman. I have information here explaining why QuickBooks Desktop (QBDT) Pro 2009 suddenly needs Windows Explorer 6.0 to operate. 

Please know that QBDT Pro 2009 was discontinued on March 31, 2011. As a result, an error can occur anytime, including the one you encountered.

Moreover, discontinued versions won't receive the latest critical security patches, updates, and Intuit services. Feel free to visit this article to learn more about the service discontinuation: QuickBooks Desktop service discontinuation policy.

To access your file, you can utilize the trial version of QBDT Pro 2024 since the 2009 version is no longer available to restore your file there. Here's how:

1. Select Open or Restore Company from the File menu.
   
2. Choose Restore a backup copy and Next.
   
3. Pick Local Backup, then Next.
   
4. Browse your computer for your backup company file. It should look like this: [Your company name].qbb.
5. Select a folder to decide where to save your restored company file. Then select Open. If you open the backup in the same folder as your existing company file, you may overwrite your data.
6. When you're ready, select Save. If you open the backup in the same folder as your existing company file, you will overwrite your data.

After restoring and updating the file, certain data can't be accessed and opened in QBDT Pro 2009.

If you wish to upgrade to a higher version, you can read this article: Upgrade QuickBooks Desktop Pro.

I'll also add this article to learn what your computer needs to experience QBDT at its best: System requirements for QuickBooks Desktop 2024.

Don't forget to comment below if you have additional questions about accessing your company's data or want to continue discussing QBDT Pro accessibility requirements. We'll be willing to help. Keep safe, and have a good one.