I'm seeing the following problem with the latest version (i.e. 1.5) of the promoted builds plugin.
Even though i tie a job on which promotions are defined to the master, Hudson is trying to execute some of the promotions on the slave(s) resulting in the following error.

Started by user <abc>
Building remotely on lnx-slave-1
FATAL: Failed to mkdirs: /opt/hudson/conf/jobs/<job-name>/workspace
java.io.IOException: Failed to mkdirs: /opt/hudson/conf/jobs/<job-name>/workspace
at hudson.FilePath.mkdirs(FilePath.java:739)
at hudson.model.AbstractProject.checkout(AbstractProject.java:977)
at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:421)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:370)
at hudson.model.Run.run(Run.java:1120)
at hudson.plugins.promoted_builds.Promotion.run(Promotion.java:74)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:123)

Error seen in the hudson UI for a promotion failing due to above error is "promotion didn't happen.......re-execute the promotion"

For now, "Andrew bayer" suggested the following workaround and it works nicely.

a.) goto "/opt/hudson/conf/jobs/<job-name>/promotions/<promotion-name>
b.) Open the "config.xml" and add the following 2 lines

<assignedNode>master</assignedNode>
<canRoam>false</canRoam>

c.) Once you add these lines, goto "Hudson->Manage Hudson" and click on "Reload configuration from the disk".
d.) Re-execute the promotion and it will work now.