while resolving my ivy.xml, I get a long list of errors, all stating "unknown resolver XYZ". I know the resolver, it is used in the same project but different task. As far as I understand, the resolver used to create the cache entry is stored and than cannot be determined by the follow-up resolver.
Question is: how can I avoid this? Seeams like this is not really an error, more like a warning since I am able to resolve all dependencies and continue compiling.
Within the same project, the build resolver will not change because it's defined in your ivysettings.xml file.
This is more likely to be a problem with a stale ivy cache. I'd suggest adding an extra target that purges your cache. Useful when encountering this type of problem:
<target name="clean-all" depends="clean" description="Purge ivy cache">
<ivy:cleancache/>
</target>