Hi,
Are you sure you used the correct url for metaweblogapi service?
If you put http://www.jaosobne.cz/novinky.aspx for the blog url then you must put http://www.jaosobne.cz/metaweblogapi.ashx for the service url.
If you put http://www.mujzune.cz/metaweblogapi.ashx its only going to show blogs for that site.
Best,
Joe