Fortunately II2LN has a built-in log system. By default will II2LN create a field with the name VCII2LN_Log in your Notes documents. This multivalue text field may contain the exact reason for the problem. However, the default level of logging is minimal, so you won't see any of the steps that II2LN perform.
You can change the log level by specifying the Import Option SetLogLevel with a value from 0 (no logging at all) to 5 (verbose logging). The import option will look something like this;
"SetLogLevel:5"
Finally you can export the log to a file on the file system, by specifying the import option SetLogFilename, like this;
"SetLogFilename:C:\Temp\Your log filename.log"
You can of course specify any filename you like.