Dateiliste

Once you wish to install Mercenary mission pack - a crap begins.

You may unpack the Mercenary mission pack installer to a separte folder, instead of bringing it at your D3 folder, which you are using;
perhaps you will have to copy some existing exe to that folder from your real D3 installation, before the installer will agree to patch that empty folder, I am not sure.

Put "merc.hog" to D3 main folder; put "merc.mn3" to missions folder.
The "main.exe" not loads "merc.hog", and that causing "unable to load level file merc1.d3l" error when trying to start "Descent 3: Mercenary" mission.

Solutions are few. If shortly - go to Method 2.

Method 1 (is not working)
Unpack "merc.hog", unpack "merc.mn3", both to the same (temporary) directory, so the content will mix.
Now pack it to "merc.mn3" pack.
Put into missions folder just this one file, instead of using of two original.
This method not works, because D3 engine dislike some extra stuff in the ".mn3".
(this method also will not help to start a mission, which is based on "merc.hog", if it could work)

Method 2
In "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" create "Descent3 Mercenary" folder.
In that folder create "UninstallString" string; value is not mandatory.
Or just use two .reg files with these contents :

Mercenary_hog_on.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Descent3 Mercenary]
"UninstallString"=""

to enable reading of "merc.hog".

Mercenary_hog_off.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Descent3 Mercenary]
"UninstallString"=-

to disable reading of "merc.hog".

Method 3
As is widely (mostly; although not by me) offered.
Install Mercenary pack; install NoCD patch; install Mercenary pack again.