Windows 7 registry %ProgramFiles% issue

I have some kind of windows appilcation, running on Windows 7 32-bit. I'm trying to register particular file extension open command with my application using windows registry. Such file extension is my own and also registered by me. The application installed in particular subdirectory within Program Files. I want my installer to register application properly for both 32 and 64-bit platfroms, since actual Program Files directory names can be different on x86 and x64 platfroms, while I need to specify path to my application, I'm using registry redirection %ProgramFiles%. Here I reproduce what records I make to registry:

// file extension
HKEY_CURRENT_USER
  Software
    Classes
      .myext
        Default REG_SZ  myapp.myext

// application
HKEY_CURRENT_USER
  Software
   Classes
    .myapp.myext
       Shell
         Open
           Command
              Default REG_SZ "%ProgramFiles%\path\to\my\app\myapp.exe" -u -i "%1"

Actual path to program files dir in my test machine is C:\Program Files With such registration I receive an error:

Windows cannot access the specified device path, or file. You may not have the appropriate permissions to access the item.

If I replace %ProgramFiles% with actual C:\Program Files everything works fine. Also when I'm using same path: "%ProgramFiles%\path\to\my\app\myapp.exe" to run application from console everything works fine too. What can be reason of such issue.

Solution

%ProgramFiles% evaluates to the 32 bit program files dir in a 32 bit process and the 64 bit program files dir in a 64 bit process. However, the location of your executable does not depend on the bitness of the shell, which is the thing that reads those registry settings. You want to write the following value to the registry:

"C:\Program Files (x86)\path\to\my\app\myapp.exe" -u -i "%1"

where I assume that is the path to the 32 bit program files dir. You should not be writing an environment variable into this registry key. Your install program will already know the full path to the executable, and you should simply write that.

One issue that I think may be confusing you is that you may be under the believe that the program files directories are subject to file system redirection. They are not.

As an aside, if you ever need to write an environment variable into the registry, and want it to be expanded upon reading, use REG_EXPAND_SZ rather than REG_SZ.