agent aspectjweaver causes ClassCircularityError

Question

I use aspects to add some targeted tracing for performance analysis. Everything used to work fine till this recent drop. Now, I get a ClassCircularityError at start-up. Note that this happens even without having any aspects in the classpath.

I am using version 1.6.6. The stacktrace is partially as follows. Is there any other information I can provide?

Exception thrown in constructor of class: '*****'. Error description: 'java.lang.ClassCircularityError: org/apache/log4j/LogManager'.
Stack trace: 'java.lang.ClassCircularityError: org/apache/log4j/LogManager
at org.slf4j.impl.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:73)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:209)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:221)
at ....

Does this have something to do with using slf4j? I am completely lost. Any help is highly appreciated.

Thanks in advance.