[rules-users] CE "not" not working

Hi, We have a few rules like the ones given below. rule "4" salience 0 dialect "mvel" when av1 : AttributeValue( str == "Boys" ) exists InventoryAttribute( attribute == "DIVISION" && value == av1 ) av2 : AttributeValue( str == "Blazer" ) exists InventoryAttribute( attribute == "SUBCATEGORY" && value == av2 ) av3 : AttributeValue( str == "Boys Upper" ) not InventoryAttribute( attribute == "CATEGORY" && value == av3 ) then VoucherSeries fact0 = new VoucherSeries(); fact0.setSeriesCode( "BUPPER1" ); fact0.setPriority(100); fact0.setRuleName(drools.getRule().getName()); insert(fact0); end The CE "not" is never evaluating to true in the above rule. The "not" CE is working only for very simple conditions like 'not AttributeValue( str == "Blazer")' . Any idea what are we doing wrong ? Regards, piyush