I guess this is some JDT limitation that is not configurable currently. The workaround is to go into the workspace preferences and set the Java->Compiler-Building /Build path problems/Incomplete build path level to warning instead of error.

Scott Stark wrote:
I'm down to 4 errors,  all of them are related to a reference to a jbossts sar artifact which the plugin apparently does not like. I'm looking to see if there is a configuration option for what are accepted jar artifacts to resolve this.

Severity and Description    Path    Resource    Location    Creation Time    Id
Illegal type of archive for required library: '/home/svn/repository.jboss.org/maven2/jboss/jbossts/jbossts-tools/4.6.1.GA/jbossts-tools-4.6.1.GA.sar' in project 'testsuite'        testsuite    Build path    1249361338466    3325343
Illegal type of archive for required library: '/home/svn/repository.jboss.org/maven2/jboss/jbossts/jbossts-tools/4.6.1.GA/jbossts-tools-4.6.1.GA.sar' in project 'thirdparty'        thirdparty    Build path    1249361338764    3325344
The project cannot be built until build path errors are resolved        testsuite    Unknown    1249361346717    3325346
The project cannot be built until build path errors are resolved        thirdparty    Unknown    1249361346666    3325345