RRules with Repeat UNTIL error

Repeat rules which are set to repeat until a specific date (using UNTIL), as opposed to repeat a certain number of times are generating a warning in iCalcreator which is expecting one of:
1) input array is a timestamp date
2) array formatted date/time
3) textual date/time

The warning (and notice) that this is generating are:
Warning: trim() expects parameter 1 to be string, array given in iCalUtilityFunctions::_setRexrule() (line 8302 of /drupal7/sites/all/libraries/iCalcreator/iCalcreator.class.php).
Notice: Undefined index: UNTIL in iCalUtilityFunctions::_setRexrule() (line 8306 of /drupal7/sites/all/libraries/iCalcreator/iCalcreator.class.php).