I've run into an issue before when upgrading the excel importer (Except that it gave me a compiler error). The issue had to do with older versions of jar files were not removed when upgrading the module. Here is a list of the jar files that come with the excel importer. I suggest going through to see if there are any duplicates with these particular jar files.
com.springsource.org.apache.commons.lang-2.5.0
dom4j-1.6.1
javax.xml.stream-1.0.1
org.apache.commons.io-2.3.0
org.apache.servicemix.bundles.xalan-2.7.1
org.apache.servicemix.bundles.xmlbeans-2.5.0
poi-3.16
poi-ooxml-3.16
poi-ooxml-schemas-3.16
replication7
xml-apis-ext
In my case, it was the three POI jar files that were conflicted. Also don't forget to clean deployment directory after you do this fix and recompile.