Word and PowerPoint File Open in Browser Error

Sometimes we get an error in Office Web Application like this:

Word Web App cannot open this document for viewing because of an unexpected error. To view this document, open it in Microsoft Word.
Error Id: e526e7cf-f17a-48ee-85ee-916c593e0569, 20110415162644

What we can see in logs? Surprise!

DownloadManager: Exception thrown downloading file \\fs001\Anikin, Alexander\Agency contract.docx: System.UnauthorizedAccessException: Access to the path ‘C:\Windows\TEMP\waccache\30091891-f580-40fb-a151-9ff2114df390\DEV_ow_services\e7c940c5-2bc8-471b-b63d-37507944b53a\’ is denied.

Sharepoint Services Pool (OWA workrs under) account can’t write into the Temp\waccache folder any more.

I’be found this, but solution 1 don’t work for me. I add permissions for this folder to my accounts and it works!

I don’t know why it happens. Conversion service use this folder for temp files, but it start creating folders without needed permissions.