Interesting. MEW opens main.css at line 138, reads 3973 bytes and leaves it opened. Later it tries to move it to recycle bin (line 237) which is unsuccessful so it tries to delete it (line 243) with no success again. It makes sense because opened file can be neither moved or deleted. File is closed at line 940.
File is probably deleted because MEW creates a new one with newer contents (MEWB301.TMP) and want to delete old and rename temp file to this one.
Questions: what is main.css file size before and after the error. Is the file changed in between? I’d like to know why MEW tries to delete it. Is is possible the file is partially loaded (File Properties, Text In Memory and the next line) — it is necessary to know the state before error. It is just a guess: I’d thinking about the reason why MEW doesn’t close file and partial load could be the reason.
I’m affaid there is some MEW bug and it is probably the same which causes David’s error; I vagually remember the scenario I saw was similar. I’ll try to find what can cause it when have time which can take several weeks.