Just a wild guess here... it seems all the paths that the script is trying to call are missing a slash after "ants", i.e.,

/usr/lib/antsN4BiasFieldCorrection

should really be

/usr/lib/ants/N4BiasFieldCorrection

So if you configured the toolkit somewhere, you might need to add a slash to the install dir or similar, or you could simply edit the antsMultivariateTemplateConstruction.sh template and insert the missing slashes there (but if the script is generated by, say, cmake, then it might get overwritten if you re-run that).

TR