please see issue http://jira.codehaus.org/browse/MNBMODULE-240 which declares the steps to reproduce with nbm-maven-plugin ut the same is true for other plugins defining custom packagings (maven-plugin packaging for example)

steps to reproduce.
 1. nbm project is created and opened.
 2. empty local repository
 3. build it with maven2, dependencies are downloaded, build successful.
 4. reload project opened in netbeans but it still stays unloadable.


the explanation is that maven2 and maven3 differ in what artifacts are skipped from downloading. The artifacts that are part of the maven core classloader (and thus the maven distro) cannot be placed on the plugin's classloader again and therefore are skipped and not even downloaded. But apparently this set differs in m2 and m3, so when the project is built with m2, the subsequent offline project loading fails as there are artifacts referenced from extension plugin that need to be present in local repo but are not.

there are multiple solutions in the ide I believe.

0. the obvious workaround that can be done on user side is to build with maven3 but it's not really obvious from the UI. and some projects or companies might only work with maven2 still.

1. somehow only require the extension plugin to be present locally and not it's dependencies, as these are unlikely to contain any metadata needed for packaging, dependency type resolutions..
2. allow both sanity build and in-JVM online project resolution
2a. somehow identify these cases and do the in-JVM resolution for the extension plugin automatically behind the scenes.