[Plugin: 3dcart: WordPress Online Store] 3dCart activation – Cannot modify header information

Have tried to install this plugin across two different installations/versions of WordPress (3.3.2 & 3.3) each using unique themes. Each install attempt returned the same php errors.

Upon attempted submission of the plugin activation settings (store url, email, etc.) form I receive the following php error ‘Cannot modify header information – headers already sent by (output started at /wp-admin/includes/template.php:1657)’. I therefore have no confirmation whether the plugin is activated/registered on the 3dCart side of things. It appears that it is though, because the widget is then enabled in the widgets panel. For reference, on the second site I tried to install this plugin on, I receive this same error, but the file it claims is causing the issue is completely different.

When I then try to incorporate the widget into my widgetised area on the shop page of the site (after having entered in all the data into the necessary fields), the following php error is echoed out on the page itself – ‘Invalid argument supplied for foreach() in /wp-content/plugins/3dcart-wp-online-store/3dcart.php on line 184’. I’m wondering whether this has something to do with the failure in the registration process of the plugin??

Regarding the ‘Cannot modify header information’ error, I have tried to deactivate all other plugins and resubmit the activation form, but this had no effect. I also read the following article – https://codex.www.ads-software.com/FAQ_Troubleshooting#How_do_I_solve_the_Headers_already_sent_warning_problem.3F The advice within it didn’t appear to resolve the issue for me. What strikes me as strange here is that the line in the template.php file that the error references as causing the problem (1657) is contained within an if ie8 conditional comment, though I’m recieving the error whilst developing using Firefox?? As such, I wouldn’t think that any problems within that section of the file could effect the site at all when using Firefox??

I’ve contacted 3dCart support (twice), but they don’t appear to be able to help, both times they’ve just directed me to this plugin installation instructions page – https://support.3dcart.com/Knowledgebase/Article/View/483/0/how-do-i-install-the-3dcart-wordpress-plugin There isn’t anything in there that addresses this issue.

Only coming here after exhausting all my own knowledge trying to resolve it, and not being able to find much other info addressing the 3dcart specific issue.

Anyway, tearing my hair out here a bit, as the deadline for this project is looming. Any help??

https://www.ads-software.com/extend/plugins/3dcart-wp-online-store/