this happened to me multiple times with the package "babel-register" which itself and it's dependencies are upgraded quite often.
It seems if a new version is published on public npm, it becomes in the internal registry only available after a few hours (caching issues?).
This led multiple times to problems with "babel-register" since some of it's transitive dependencies could not be found during installation and I get in npm errors like that:
00:03:37.265 INFO: npm ERR! node v0.12.4
00:03:37.265 INFO: npm ERR! npm v2.10.1
00:03:37.265 INFO: npm ERR! code ETARGET
00:03:37.265 INFO:
00:03:37.265 INFO: npm ERR! notarget No compatible version found: babel-code-frame@'>=6.7.2 <7.0.0'
00:03:37.265 INFO: npm ERR! notarget Valid install targets:
00:03:37.265 INFO: npm ERR! notarget ["6.0.0","6.0.2","6.0.12","6.0.14","6.0.15","6.1.4","6.1.5","6.1.6","6.1.7","6.1.8","6.1.9","6.1.10","6.1.11","6.1.12","6.1.13","6.1.14","6.1.15","6.1.16","6.1.17","6.1.18","6.2.4","6.3.13","6.5.0","6.5.0-1","6.6.0","6.6.5"]
00:03:37.265 INFO: npm ERR! notarget
00:03:37.265 INFO: npm ERR! notarget This is most likely not a problem with npm itself.
00:03:37.265 INFO: npm ERR! notarget In most cases you or one of your dependencies are requesting
00:03:37.265 INFO: npm ERR! notarget a package version that doesn't exist.
00:03:37.265 INFO: npm ERR! notarget
00:03:37.265 INFO: npm ERR! notarget It was specified as a dependency of 'babel-core'
00:03:37.265 INFO: npm ERR! notarget
I unfortunately cannot get you easily diagnostic information, but I'm optimistic you can reproduce the issue by publishing a new version of a package on public npm and then try to install it immediately via private nexus proxy.
Best Regards Christian