If the file you are copying is larger than 4GB you may be hitting file system limits. In my experience, the errors produced when hitting file system size limits are usually about permissions or disk space. Especially check if you have a fat32 or vfat file system that you are copying from or to.
Just a thought and avenue to explore. For example, if you are trying to copy a file larger than 4GB, switch to trying to copy a smaller file. If the smaller file works, you know the larger file size is part of the problem you are seeing.
Alan