recompiling pixmap.bmx

I want to access to 8 bit informations of alpha in pixmap module. I convert, in the "pixel.bmx" file this:
Global AlphaBitsPerPixel[]= [0,0,8,0,0,8,8]
by
Global AlphaBitsPerPixel[]= [0,0,0,8,8,8,8]
But, when i try to recompile the pixmap module with the command line:
"bmk makemods -r brl.pixmap"
it's every time write me an error, even if i let the original pixel.bmx file.
Does anybody know why?

delete everything in your mod folder then run syncmods again. That should fix the error.

that work, thank's ;o)

No, i'm sorry, but it's continue to crash.
It's write:

Archiving:pixmap.d.a
'ar' is not recognized as an internal or external command,

Even if i just recompile the pixmap.mod without made any changes.