When I open some files in Winamp and in Mp3tag it seems like some informations are missing. For example, as you can see Winamp puts out an album interpret (ID3v2) while Mp3tag does not. Whats the problem?
Indicates that you have more than one field of the type YEAR in your file. See the extended tags dialogue (Alt-T) to check that.
If you do not see information but expect it ...
check which tag versions you have in the file. Out of sync APE tags usually lead to confusion. See also Tools>Options>Tags>mpeg which tags you read, write and delete. See this thread on the priority of tags in MP3tag.
check if the player has its own database and is rather reluctant to write that information to the files, if you used the player as tagger.
check if the player has to update its cache so that it shows the uptodate information.