"java.lang.IllegalArgumentException: Sniffers with type [connector] and type [ejb] should not claim the archive at the same time. Please check the packaging of your archive"
In my case it happens when I deployed a web archive out of Eclipse directly into a running GlassFish instance on my machine using the GlassFish plugin.
I tried a Google search for this error and found a blog posting by Adam Bien describing this error and a solution. Well, indeed my packaging was wrong. I accidentally bundled the artifact glassfish-embedded-all into my WAR archive and this was causing the trouble.
The solution is very simple: Either change the scope in your pom.xml to "provided" or - in case you don't need the dependency - remove it from the dependency section of your pom.
In my case it turns out that the dependency was not necessary anymore and I deleted it.