Without having a URL of the page you're trying to validate and being able to see the source, here are some guesses.
In /modules/mod_sclogin/tmpl/joomlaLogin_vertical.php, try replacing
#1. Around line 27
<input name="username" tabindex="0" id="sclogin-username" class="input-block-level" alt="username" type="text"
with
<input name="username" tabindex="0" id="sclogin-username" class="input-block-level" type="text"
#2. Around line 36
<input name="<?php echo $passwordName; ?>" tabindex="0" id="sclogin-passwd" class="input-block-level" alt="password" type="password"
with
<input name="<?php echo $passwordName; ?>" tabindex="0" id="sclogin-passwd" class="input-block-level" type="password"
#3. Around line 56
<input id="sclogin-remember" type="checkbox" name="remember" class="inputbox" <?php echo $helper->getRememberMeValue();?> alt="Remember Me" />
with
<input id="sclogin-remember" type="checkbox" name="remember" class="inputbox" <?php echo $helper->getRememberMeValue();?> />
#4. Around line 63
<input id="sclogin-remember" type="hidden" name="remember" class="inputbox" <?php echo $helper->getRememberMeValue();?> alt="Remember Me" />
with
<input id="sclogin-remember" type="hidden" name="remember" class="inputbox" <?php echo $helper->getRememberMeValue();?> />
If that works, I'd recommend creating a template override for this file so you don't lose any changes on upgrade of SCLogin.
-Melissa