When submitting comment form Fatal error: Class 'Api' not found

Question

My problem: I could submit a comment, but the data wouldn´t be saved into the database. But no error message was shown. After submisseion EE would just take the comment, throw it away and then would show the SE-page again.

Checked around, found this tip here on EESE, got rid of the NSM htaccess generator. Now I´m back to the normal index.php-Syntax.

Now I can submit Comments, but I get the following error message, when I submit a comment as a logged in user

Fatal error: Class 'Api' not found in {removed}/system/expressionengine/
libraries/api/Api_channel_fields.php on line 3

When I comment as a non-logged in user I just get a blank page.

But the comments are saved. I can see and edit them in the CP and the comments are attached to the respective entry. So, the process works, I "just" need to get riod of the error message and have EE return to the SE-page.

I tried to set the return value as

return="entry/index/url_title"

but this didn´t work.

I checked the Api_channel_fields.php. This is what I see in line 3

class Api_channel_fields extends Api {

I even uploaded a fresh Api_channel_fields.php from my installation package. Nothing helped. Any thoughts, how I can fix that? I would love to get the .htaccess back to work, but for now I´d be happy to just get rid of the fatal error

Edit to answer Adrian Macneil questions

What other plugins/extensions are you using? 1. BW Channel Count 2. Channel Videos 3. Content Elements 4. Developer 5. HJ Social Bookmarks 6. Entry Type 7. httpHeader 8. ImageSizer 9. Low Nospam 10. Low Replace 11. Low Seg2cat 12. Minimee 13. NSM Morphine 14. PDF Press 15. PT Fieldpack 16. Recent Entries 17. Republic Variables 18. SuperGeekery Tag Stripper 19. Sitemap 20. Taggable 21. Template Variables 22. TruncHTML

Are you using the built in EE comment form? Yes, I copied the code from the EE help pages and adapted it. The comment module is on. This is my template code

{exp:comment:form channel="artikel"}
    <fieldset>
    <legend>Ihr Kommentar</legend>
        <label for="name">Name (erforderlich)</label> 
        <input type="text" name="name" value="{name}"/>
        <label for="email">E-Mail (erforderlich, wird nicht ver&ouml;ffentlicht)</label>
        <input type="text" class="twelve" name="email" value="{email}" />
        <label for="url">Web-Site</label>
        <input type="text" class="twelve" name="url" value="{url}" />
        <label for="comment">Ihr Kommentar</label>
        <textarea name="comment">{comment}</textarea>
        <input type="submit" class="button" name="submit" value="Kommentar absenden" />
        <p>&nbsp;</p>
    </fieldset>
{/exp:comment:form}

This is the code as it is rendered on the SE-page

<form id="comment_form" method="post" action="http://www.bandikutmedia.de/eintrag/journalisten-auf-die-rote-liste"  >
    <div class='hiddenFields'>
        <input type="hidden" name="ACT" value="1" />
        <input type="hidden" name="RET" value="http://www.bandikutmedia.de/eintrag/journalisten-auf-die-rote-liste" />
        <input type="hidden" name="URI" value="eintrag/journalisten-auf-die-rote-liste" />
        <input type="hidden" name="PRV" value="" />
        <input type="hidden" name="XID" value="31203ae5e27a3ba65d1cbaec73d7ae6ea2ba9fc8" />
        <input type="hidden" name="entry_id" value="33" />
        <input type="hidden" name="site_id" value="1" />
    </div>
    <fieldset>
    <legend>Ihr Kommentar</legend>
        <label for="name">Name (erforderlich)</label> 
        <input type="text" name="name" value=""/>
        <label for="email">E-Mail (erforderlich, wird nicht ver&ouml;ffentlicht)</label>
        <input type="text" class="twelve" name="email" value="" />
        <label for="url">Web-Site</label>
        <input type="text" class="twelve" name="url" value="http://" />
        <label for="comment">Ihr Kommentar</label>
        <textarea name="comment"></textarea>
        <input type="submit" class="button" name="submit" value="Kommentar absenden" />
        <p>&nbsp;</p>
    </fieldset>
</form>

Answer 1

Ok- so the issue for me turned out to be "Content Elements" plugin from Krea. After disabling this, the errors went away!

Answer 2

Please download new Content Elements 1.1.1 release: http://devot-ee.com/add-ons/content-elements

We have fixed problem with comments.

Thank you, team Krea