rem: this.mProperties.deleteProperty(aName); 
add: try { this.mProperties.deleteProperty(aName); } catch (e) { } 
context:     deleteProperty: function (aName) {        if (this.mImmutable)            throw Components.results.NS_ERROR_FAILURE;        this.mProperties.deleteProperty(aName);    },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/b4a3b00ed58fa70e21c7fdade2185d7787d28428/calItemBase.js/clean/calendar/base/src/calItemBase.js