Now, I don't have the 737 experience or these KLM textures. But I can assume it is aliasing a model folder that isn't there. Change the part in the KLM section where it lists the model it is aliasing to, to the model that exists in the main aircraft folder.

For example:
[fltsim.0]
title = Antonov An-72
sim = Antonov An-72
model =klm
panel =
sound =
texture =
panel_alias =
sound_alias =
kb_checklists = CheckList_Antonov_An-72.txt
kb_reference =
ui_manufacturer = Antonov
ui_type = An-72
ui_variation = Aeroflot
description =
There exists no klm folder in your aircraft. There only exists a folder with (example here) named 737. You would then modify the model section to say:
[fltsim.0]
title = Antonov An-72
sim = Antonov An-72
model =737
panel =
sound =
texture =
panel_alias =
sound_alias =
kb_checklists = CheckList_Antonov_An-72.txt
kb_reference =
ui_manufacturer = Antonov
ui_type = An-72
ui_variation = Aeroflot
description =
Hope this helps.
