The QBWinstance Handle error is one that Intuit has not yet properly acknowledged or fixed. Please do add your voice and contact Intuit support about this.
Make sure QB is fully patched. Where I am, the latest revision is R4 and includes a revised printer DLL that was causing problems (for me at least).
Try new printer drivers for the printer that is causing problems.
It looks (above) as if you have more that one QBW file. I have found it is best to close a file and then exit QuickBooks completely before opening a new file.
These are all workarounds in my opinion, but it is how I have to use QuickBooks on Windows 7.
... Thinkpads_User
