WiX on Windows XP: Failed to initialize built-in variable value 'ProgramFilesFolder'

I haveI have an installer built with WiX 3.6 (beta) which works fine on Windows 7, but on Windows XP the install fails. The end of log file in %TEMP% is:

Apply begin
Setting string variable 'ProgressPackageName' to value 'Product'
Error 0x80004005: Failed to get known folder.
Error 0x80004005: Failed to initialize built-in variable value 'ProgramFilesFolder'.
Error 0x80004005: Failed to get variable: ProgramFilesFolder
Error 0x80004005: Failed to set variable value.
Error 0x80004005: Failed to format value '[ProgramFilesFolder]\Company\Product' of variable: InstallFolder
Error 0x80004005: Failed to set variable value.
Error 0x80004005: Failed to format property value.
Error 0x80004005: Failed to add properties to argument string.
Error 0x80004005: Failed to execute MSI package.
Error 0x80004005: Failed to configure per-machine MSI package.
Error 0x80004005: Failed to execute MSI package.
Error 0x80004005: Failed to execute apply.
Error 0x80004001: UX cannot erase variables by passing a NULL string, yet.
Error 0x80004001: UX cannot erase variables by passing a NULL string, yet.
Apply complete, result: 0x80004005 restart: No
Shutting down, exit code: 0x80004005

I haven't found anything on Google about problems with XP and WiX 3.6 (and it seems unlikley that it just wouldn't work with XP, but it is beta after all).

What can I do to try and solve, or at least do to gain more information on what might be going wrong here.

Looks like a bug in Burn. Please file a bug with details (e.g., version of XP, which build of WiX) at https://sourceforge.net/tracker/?group_id=105970&atid=642714.