This is caused by the iOS keyboard sending smart quotes. Here are a few things you can try:
You could long-press on the quote and apostrophe keys on the keyboard and choose the simple apostrophe (') and quote (") characters.
You could send smart quotes to the MUD by changing MUDRammer’s encoding in MUDRammer Settings -> Advanced -> Encoding to a unicode encoding like UTF-8. MUDRammer will now send those characters correctly, but if the MUD does not support unicode, the MUD still won’t recognize those characters. You should check with your MUD to be sure.
You could always send simple quotes by disabling smart punctuation in iOS Settings -> General -> Keyboards -> Smart Punctuation OFF.