Problem with sonar-maven-plugin-1.8

Hello;

I'm trying to get Sonar 1.8 up and running on a private intranet.   I've got the web-app deployed, the database created, Nexus all configured, and am trying to get the sonar-maven-plugin working.    But I'm getting the following error during the process:

mvn clean install org.codehaus.sonar:sonar-maven-plugin:1.8:sonar

BUILD ERROR

Can not execute Sonar

Embedded error: Unable to find the mojo 'org.codehaus.sonar.runtime:sonar-core-maven-plugin:20090609145257:internal' in the plugin 'org.codehaus.sonar.runtime:sonar-core-maven-plugin.

When I navigate to the repo in Nexus, the sonar-core-maven-plugin is there, both the pom and the jar file.  I suspect the problem is the 'internal' part of the plugin descriptor, but not sure how to get rid of this.

We're using JDK 1.5.0_16, Maven 2.0.9, Nexus 1.3.4.

It's downloading other plugins, because I see earlier in the session messages like
Downloading: http:......./org/codehaus/sonar/runtime/jdbc-driver/mysql-connector-java-5.0.8/....pom

No, I can't post the full output of the command, and no, I can't go up to a new version.
Any help would be appreciated.

Bob Yetman