Could not initialize class com.rb.core.services.event.a480 -

I'm getting this error in a variety of conditions in Private Cloud with Custom Triggers trying to import an Excel file (to an object that does not have a Custom Trigger.  Apparently Rollbase is trying to load a Trigger class and is not finding a Config class.  Unfortunately, the trace does not identify the Trigger class being loaded.

Now for the strange part - this only happens with a XLS file.  When I run the same import with a CSV file, I do not geterrors.

Any ideas on how to resolve this?  Note:  Only two custom triggers exist and they work in all other situations.

Here's the specific trace:

java.lang.NoClassDefFoundError: Could not initialize class com.rb.core.services.event.a480
	at com.rb.core.services.event.TriggerDef.getConfig(TriggerDef.java:106)
	at com.rb.core.services.event.a482._x23(a482.java:430)
	at com.rb.core.data.a363.getTriggerDefs(a363.java:936)
	at com.rb.core.services.event.a482.getTriggerDefs(a482.java:450)
	at com.rb.core.services.event.a482.hasTriggers(a482.java:142)
	at p8.a569.actualImport(a569.java:157)
	at p8.a569.doJob(a569.java:110)
	at p40.a225.doJob(a225.java:33)
	at com.rb.util.system.a170.run(a170.java:52)