when I try to save the point ... Property Identifier field can't take the Present Value why ?
I'm not sure what you mean. If you wanted to use a different property you would have to press the green refresh arrow, as the old UI didn't automatically look up what property types were possible for a given object type.
plz tell me how can I fix this error ??
It may be easier with the stacktrace right below what you have shown in the image, but, the first thing to try is deleting your Mango/work/jsp directory. This has the compiled JSPs, which this error is certainly related to. Alternatively you could use the new UI, as BACnet is supported on the new data sources page in 3.6 already.