[vt74] Fatal Error when migrating from vt73 to vt74 in log4php library - Class 'LoggerPatternParser' not found

When executing index.php?module=Migration&view=Index&mode=step1 you get:

Fatal error: Uncaught Error: Class 'LoggerPatternParser' not found in /vt/libraries/log4php.debug/layouts/LoggerLayoutPattern.php:152 Stack trace: 

#0 /vt/libraries/log4php.debug/config/LoggerPropertySetter.php(155): LoggerLayoutPattern->activateOptions() 
#1 /vt/libraries/log4php.debug/config/LoggerPropertySetter.php(114): LoggerPropertySetter->activate() 
#2 /vt/libraries/log4php.debug/config/LoggerPropertySetter.php(86): LoggerPropertySetter->setProperties(Array, 'log4php.appende...') 
#3 /vt/libraries/log4php.debug/LoggerPropertyConfigurator.php(633): LoggerPropertySetter::setPropertiesByObject(Object(LoggerLayoutPattern), Array, 'log4php.appende...') 
#4 /vt/libraries/log4php.debug/LoggerPropertyConfigurator.php(560): LoggerPropertyConfigurator->parseAppender(Array, 'A1') 
#5 /vt/libraries/log4php.debug/LoggerPropertyConfigurator.php(434): LoggerPropertyConfigurator->parseCategory(Array, Object(Logg in /vt/libraries/log4php.debug/layouts/LoggerLayoutPattern.php on line 152

notice the error is the folder log4php.debug. Not sure what the .debug means.

refreshing the page will continue the migration without further problems.