Description of problem:

A timer execution can fail with  exception if the Timers Info object (which is custom code) contains characters which are relevant for String.format replacement:
java.util.UnknownFormatConversionException: Conversion = '!'
        at java.util.Formatter.checkText(Formatter.java:2547)
        at java.util.Formatter.parse(Formatter.java:2533)
        at java.util.Formatter.format(Formatter.java:2469)
        at java.util.Formatter.format(Formatter.java:2423)
        at java.lang.String.format(String.java:2792)
        at org.jboss.as.ejb3.timerservice.TimerImpl.toString(TimerImpl.java:568)
        at java.lang.String.valueOf(String.java:2849)
        at java.lang.StringBuilder.append(StringBuilder.java:128)
        at org.jboss.as.ejb3.timerservice.TimerServiceImpl$TimerCreationTransactionSynchronization.afterCompletion(TimerServiceImpl.java:1106)

How reproducible:
Create a timer which include an InfoObject that contains "%!" if toString() is called.
Enable DEBUG/TRACE for the ejb timers or force a failure in timeout is invoked.
Both should use the toString() method and fail.