<p>I have written some code in my VB.NET application to send an HTML e-mail (in this case, a lost password reminder).</p>

<p>When I test the e-mail, it gets eaten by my spam filter.  One of the things that it's scoring badly on is because of the following problem:</p>

<pre>MIME_QP_LONG_LINE  RAW: Quoted-printable line longer than 76 chars</pre>

<p>I've been through the source of the e-mail, and I've broken each line longer than 76 characters into two lines with a CR+LF in between, but that hasn't fixed the problem.</p>

<p>Can anyone point me in the right direction?</p>

<p>Thanks!</p>

Quoted printable expands 8 bit characters to "={HEX-Code}", thus making the messages longer. Maybe you are just hitting this limit?
Have you tried to break the message at, say, 70 characters? That should provide space for a couple of characters per line.
Or you just encode the email with Base64 - all mail client can handle that.
Or you just set Content-Transfer-Encoding to 8bit and send the data unencoded. I know of no mail server unable to handle 8bit bytes these days.