Windows XP in VMware Workstation: Default Host Application Error

I was running a Windows XP SP3 guest in VMware Workstation 7.1 on an Ubuntu 10.04 (Lucid Lynx) host.  When I tried to open a PDF file in the VM, I got a Default Host Application error message:

Default Host Application
Make sure the virtual machine's configuration allows the guest to open host applications.

A search for that sentence turned up no hits.  A modified search turned up only a few.  One thread led me to right-click on the PDF and select Open With.  There, for the first time ever, I saw the VMware icon and "Default Host Application" at the top of the list, labeled as the Recommended Program.  I clicked OK, but this put me back to the Default Host Application error message.  I guessed that maybe the problem was that I had already told Ubuntu to use Adobe Reader for Ubuntu (or maybe some other program) to be the default application for PDF files.  I had meant that to apply only when I was in Ubuntu, not when I was in a WinXP VM.  I checked VM > Settings > Options tab > Guest Isolation, and it did not have the box checked to "Enable VM communication interface (VMCI)."  So that seemed to be prohibiting the host (Ubuntu) from using its own default program to open the PDF when I was in the guest (WinXP).

The VMware Workstation 7.1 User's Manual made me wonder whether I had slipped into Unity mode, but I checked Workstation's View menu pick and, no, the setting was Autofit Guest.  I tried Open With again, but this time I browsed to the program that I wanted to use to read PDFs.  At this point, that program was Sumatra PDF.  But after I clicked on the Sumatra PDF .exe file, I was back at the Open With, and it had not remembered what I had just done.  I did it again; same result.  I tried WordPad instead.  It rendered the PDF as what looked like an XML file.  I closed that, went back to right-click > Open With, and this time the VM Default Host Application and WordPad were the only two programs listed.  Still no luck with Sumatra.  Another post made me think this was actually intended behavior, under the concept of "application sharing."  I didn't pursue that at this point.

In Windows Explorer, I went to Tools > Folder Options > File Types, scrolled down to the PDF file type, clicked Change, navigated to Sumatra . . . but still the same result:  it didn't remember what I had selected.  Following a tip, I went to Start > Run > CMD and typed "assoc .pdf."  This told me that the PDF file type was associated with pdf_auto_file.  A corresponding search led to the suggestion to go back into the File Types list, down to PDF, and click on Restore to reset it to the Windows default program for PDFs.  Now it wasn't set to run with anything.  I clicked on Change and navigated to Sumatra again, but it still didn't remember it.

The Microsoft Support page didn't seem to address this situation.  Ramesh, however, did provide an OpenWithAdd utility that added Sumatra to the Open With list.  After that, double-clicking on the PDF file opened the Open With list, with Sumatra PDF highlighted.  I clicked on the "Always use the selected program to open this kind of file" box and then OK.  I killed Sumatra, double-clicked on the PDF again, and this time Sumatra opened right up.  Problem solved!  Another way of doing it, if I hadn't wanted to run the OpenWithAdd utility, was apparently to use this registry edit:

[HKEY_CLASSES_ROOT\.pdf]
@="AcroExch.Document"

When I went to that location in my registry, I saw that it was still set to pdf_auto_file, so I made that change.  I wasn't sure whether that would have eliminated the need for the OpenWithAdd utility.