dhtmlxCalendar [line 1344 - Error]

I am using the pro version of dhtmlxCalendar and have added it to a custom SharePoint aspx page. All works great apart when I refresh the page in IE6 I get the following error message:

Line 1344
Error: Object doesn’t support this action

The code it fails on is as follows:

// marker
this.i[a]._dhtmlxcalendar_uid = null;
delete this.i[a]._dhtmlxcalendar_uid; <------ This is where the error is rasied as this.i[a]._dhtmlxcalendar_uid = null;

Is this a bug in the js librray?

Many thanks.

Unfortunately the issue cannot be reconstructed.
Please, provide any kind of sample to reproduce the issue.