The MANIFEST.MF of slf4j-log4j12 contains an improper Import-Package that prevent the bundle from loading :
Import-Package: org.slf4j;version=${parsedVersion.osgiVersion}, org.slf4j.spi;version=${parsedVersion.osgiVersion}, org.slf4j.helpers;version=${parsedVersion.osgiVersion},, org.slf4j.event;version=${parsedVersion.osgiVersion}, org.apache.log4j
There is two comma at the end of the third line.