IDE does not open file

Did anyone had problems when trying to open a source file in the IDE?
Certain files can not be opened!
In one file (which I edited before with the jed editor) was a î - sign.
After removing this sign the file could be opened.
I had the same proble with another file, but here I could not see the
signs. Must have been something like control chars.
In jed I never had problems, just in the IDE the files can not be opened.
Anybody an Idea whow to avoid this? I tried to select another charset, but
that did not help.