I have a form with all the same values on a page of my site that matches one found on a Marketo landing page I created. I moved the HTML and form styling to the new page, and also the JavaScript. I use Grunt to compile my JS, so it was moved from a page_company module to a page_contact module.
I DID modify the values for options in the <select> field mentioned in my initial post. But I made sure that these values were also updated in Marketo.
Field as seen in Marketo:
<select class="mktFormSelect mktFReq" name="ReasonforContact" id="ReasonforContact" size="1" tabindex="5">
<option value="Sales inquiry" selected="selected">Sales inquiry</option>
<option value="Training">Training</option>
<option value="Technical support">Technical support</option>
</select>
Corresponding site field:
<select class="mktFormSelect mktFReq form-control" name="ReasonforContact" size="1" style="display: block; height: 36px">
<option value="Sales inquiry" selected="selected"> Sales </option>
<option class="register-default" value="Training"> Training </option>
<option value="Technical support"> Technical Support </option>
</select>
One update: a test form submission (using one of the other <selection> options - Technical support) that wasn't returning an error DID successfully show up in my Lead Database. This must mean that the issue is specifc to the "Sales inquiry" <select> option that's returning the "Please select a value for this field." But if the field attributes on my site match the same field attributes in Marketo, what could be causing the issue?