I expect that something is still using this module. Does adding --verbose to the modprobe command give more informations?
modprobe -r -v ndiswrapper
Perhaps there is information with the docs that might be enlightening: /usr/doc/ndiswrapper-kernel-1.59
There is also the ndiswrapper-utils package.
I am assuming you are using the SBo package for ndiswrapper, but that may not be the case.