Cant remove cover from metadata

Hi, I have a problem with windows 7 not capable of reading metadata of some of mine mp3 files. They play in all of my players (including WMP), but windows cant read the data and I wanted to find out why.
In songbird I found out that problematic files have covers so that would be the problem and I wanted to remove them but I couldn't because it didn't work. I tried mp3tag and it doesn't work also. Remove cover works but when I select the song again its still there. I can't change other meta data, it says "cannot be opened for writing" but I don't think that those files are read-only.
Thx for help.

You are not very specific about which program does not show the desired behaviour.
WIndows 7 Explorer does not read V2.4 tags properly.
WMP maintains a library and a thumbnail cache which may pretend that there are still covers in the files.
mp3tag shows fairly reliably the data in files.
But if you have set that APE tags can be read and your files have these then they overwrite all other tags in the display. Get rid of these tags.
(BTW: why do you want to get rid of the covers? This forum is full of requests to find the covers more or less automatically, so the general trend definately goes to files with embedded cover art)

Nevermind, after reboot I was able to change metadata, problem was that year ago some retarded music player downloaded the covers and changed the version to ID3v2.4. And mp3tag seems to change them back just by selecting tracks.
I still don't understand why I can't remove those covers but I don't care anymore.

Mp3tag doesn't change tag information when selecting tracks. It's not possible.

well not by selecting, but for example you click on title and it shows you input but when I press enter and not change anything it changes ID3 to ID3v2.3 (ID3v1 ID3v2.3). That seems to be default in options under mpeg, I didn't change anything in there.

Well, you have described a classic example of misuse.
You should learn more intensively how to use the user interface of a machine.

It is a well-known agreement and understanding when dealing with machines, that pressing [Enter] is a commitment to the machine to perform the currently available prepared action.
In general, pressing [Enter] confirms a change in an edit field or confirms the executing of a pre-selected button field.

If you open an edit field, regardless if the current content will be changed or not, and you leave the field by pressing [Enter], then all subsequent related internal processes will be executed.
If you open an edit field, regardless if the current content will be changed or not, and you leave the field by pressing [Esc], then all inputs and subsequent related internal processes will be discarded.

When editing a cell in the Mp3tag list view, the change will be executed immediately against the underlying file, when leaving the cell by pressing [Enter].
This action also includes the saving of the file with the currently specified tag types.