I've bought GWFP, instaled it, but it's not working. At Jomres admin it is written:
"SimpleXML is required for this plugin to work properly."
Can you help me, please?

you have to ask your hosting provider to install/enable SimpleXML on your server.

The hosting provider says, it's installed and enabled. Is this message in Google Weather general ?

what do you mean?

I have a message in admin Google Weather:

"This plugin displays current weather information and forecast for the next 3 days in property details page, based on property town and country. The language in which the information is displayed is selected automatically, based on active language.

SimpleXML is required for this plugin to work properly."

Is this message in any GW instalation, or it means, that is something with SimpleXML wrong?

The message is there on all installations. Nothing is wrong.