I use OS X, and so for those rare cases where I must deign to run a program designed for Windows I make use of my copy of it hosted in Parallels Desktop. Now, Parallels has been generally good to me, but I recently came across the problem documented in this forum thread where its ability to launch Mac applications from Windows caused some basic file associations in Windows-land to stop working. For example, Excel files were listed as “xls_auto_file” by Explorer and double clicking on them only gave me the “Open With” dialog: not very helpful.

The thread does suggest a means of solving the problem, by creating a batch file that re-associates a white-list of some of the possibly affected extensions, like this:

REM Restores MS Office File Type Associations
assoc .doc=Word.Document.8
assoc .dochtml=wordhtmlfile
assoc .docmhtml=wordmhtmlfile
assoc .docxml=wordxmlfile
assoc .dot=Word.Template.8
assoc .pot=PowerPoint.Template.8
assoc .pps=PowerPoint.SlideShow.8
assoc .ppt=PowerPoint.Show.8
assoc .rtf=Word.RTF.8
assoc .wbk=Word.Backup.8
assoc .xlc=Excel.Chart.8
assoc .xlm=Excel.Macrosheet
assoc .xls=Excel.Sheet.8
assoc .xlt=Excel.Template
assoc .xlw=Excel.Workspace


However, this felt a bit ad-hoc to me, and in particular some of the extensions that were affected for me were not on the list. Thus, like any good programmer I went off and whipped up a utility designed to undo the damage inflicted on my poor defenseless HKEY_CLASSES_ROOT by Parallels.

Using it is pretty simple: just click “Scan” and then “Fix Selected” repeatedly until the scan finds nothing more of interest. Now, before I give you a download link to the utility, I need to give you the standard disclaimer to which you must agree in order to use it:

This utility is provided on an ‘as is’ basis, without warranties of any kind, and no warranty, express or implied, is given that the operation of the utility is correct or safe to use. I do not accept any liability for any error or omission. Use of the utility is at your own risk.

Sorry for the legalese but this utility is modifying your registry and hence (though I feel it is highly unlikely) could get something quite, quite wrong. You would be also wise to have a backup of the HKEY_CLASSES_ROOT registry branch to restore in case you aren’t happy with the changes made by the utility.

That said, without further ado here is the utility and its source code (C# 3.0), both of which (being of my sole authorship) I release into the public domain. I hope someone else finds it useful!