Newsletter sending but weird characters being displayed in admin

When the email sends, I get these weird symbols, this is sending just one email, but if i send it to all newsletter subscribers I get thousands of these characters. Any idea what is causing it?

Newsletter and Product Notifications Manager
Please wait .. sending emails ..

Please do not interrupt this process! ¬\MOÂ@¼ó+^4!ô@¥#ØèA¢‰'5áhZZhì"F?Þ7oÛm·%&8°‡Ýe?fØ÷º0c¶ø¨ ´§‹wYÒÅ«Ñå¿1-ØülH¬nNNg³¿¼Qâùã4K×I•ÐI ¸V+áÐÿ¨c{ArÔãÈ¥Þ}0M´%Q¨¾à™"‰Èš<š.sÿ©³ £¥Öáí—ÊËD1Ü̃ÈÛ’»u1gÛ+ Kö{®xï^¬Ø$˜ãEþÁRæVWkŸv䶳ÿ BiYÏ'fJmŒ³Á^)…W©SduvŽ†ÉÏß9ñ…ÏBãA!r£‹xÐŒÚGo˜þ4E¢ ÖÉxo®äçJC!ûÏO†ñ*£8ŠHh«ÝŠvš¨Õ"ª¢¦±©œP äb^.—Údžº°—Ò9V}Q·\‡¥¬ïò—&Š‡•´¿÷22ðOϽp¯‚3]–Ì3*IT%L5y•¹p3ð%,ˆüÎÿÿÊÌö;ÓU

This is what the source code shows

<td class="main" valign="middle"><b>Please wait .. sending emails ..<br /><br />Please do not interrupt this process!</b> 
<div class="systemError">1065 Query was empty<br />in:<br />[]<br />If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.<br /></div>

Any ideas?