Okay, moved from
Vista: Fehler beim Programmaufruf to this forum.
2
Lefteous
I don't think, that this is fixed with any existing MS-SP. As mentioned in the above thread, the phenomenon, is still here under Vista ultimate, also the update state is very close to
Herr Mann's report.
Let's try to locate the reason with a little bit more systematic testing.
The Beta4 has one different behavior compared to Beta3:

When copying the avi-filename to the TC - Command line and executing it from this place (<Ctrl+Enter><Enter>), always the correct associated program is called. This is definitly different to TC7b3.
In Beta 3 this method works only when WindowsMediaPlayer(WMP) is the default program.
Identical behavior in Beta3 and Beta4:

Double Click or <Enter> neither works in B3 nor B4 if the default program is not WMP.

Context menu and selecting the first entry works with both betas and both associated programs.
If WMP is the default program the entry is named "play"
If mPlayerC is the default program, the entry is identical to the "filename"

dragging the avi file on an new button and start the the document with a click on this buttons works only with WMP, not with mPlayerC declared as default program
Interesting remark: under "icon file" the filename of the actually associated program is automatically inserted.
So we have 4 different methods to open a document.
In Beta3 only one of four is okay.
IN Beta4 two of four are okay.
Knowing TC's source code, following the different execution paths, it should be possible to find the one working solution to fix this behavior under Vista.
HTH
Holger