Error handling when calling update_item_instance

Can anyone give advice on why I'm not getting an error message returned from a call to update_item_instance?  The code below returns the following blank error information:

*** ERROR *** API call to null extended attributes failed.        --- my own text
Rolling back all changes for this IB instance.                         -- my own text
x_msg_count is 1
x_msg_data is
x_return_status is E
error msg is:                                                          -- you'll see that it returns a big nothing. 

Thanks for your help -- maybe another set of eyes can spot an error.  I've never had a problem getting data from fnd_msg_pub.get() in other subsystems, but am tearing my hair out with it in the Install Base module.  For ex, in the other modules, the manuals say to read the message text directly if the message_count is 1; I've not found that this works in IB.