There's an open issue #1527 targeting this problem (Guava 15 cannot be deployed to any JEE6 container) which occured after fixing this one. Please star and / or comment and wait for the fix (comment #33 suggests that version 15.0.1 could be released in near furture).
EDIT: Meanwhile, the issue was resolved by new maven release:
A note on JEE6 / CDI 1.0
A workaround added in Guava 15.0 to make it compatible with CDI 1.1 (used in JEE7 containers) caused problems for Guava with CDI 1.0 (used in JEE6 containers).
If you're using Guava in a CDI 1.0 environment, you should use guava-15.0-cdi1.0.jar instead of the normal Guava jar. In Maven, the dependency can be specified as:
<dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>15.0</version> <classifier>cdi1.0</classifier> </dependency>
If you want to deploy on both JEE 6 and 7 servers, you must use Guava 13 or wait until 16 is released.