The form you submitted contained the following errors file_upload: This field is required. File_Upload: This field is required

I have a channel form from which guests can upload all files. Every other field works fine except for the file one. My file directory is named “content”. My manual input code in the template looks like this

<input type=”file” name=”file_upload” /> <input type=”hidden” name=”content” value=”1” />

This is the error I am getting: The form you submitted contained the following errors file_upload: This field is required. File_Upload: This field is required

Any ideas?