AJAX error when adding Renderable Block to Panel

When I attempt to add a block to a panel, if the block returns a string it works fine, but if the block returns a render array I get the following error:

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Message from webpage
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An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /panels/ajax/editor/add-pane/panel_context%3Apage-main_libraries_home_page%3Apage_main_libraries_home_page_panel_context/upper-center/block/display_catalog_searches-search_tabs/form
StatusText: OK
ResponseText: Warning: strlen() expects parameter 1 to be string, array given in /var/www/mainweb/includes/bootstrap.inc on line 1587
Notice: Array to string conversion in /var/www/mainweb/includes/common.inc on line 1442
[{"command":"settings","settings":{"basePath":"\/","pathPrefix":"","ajaxPageState":{"theme":"seven","theme_token":"mv4eOIRRwrdsqhC8kPNSblzyzqIxOKpASZGe4JckA_w","css":{"misc\/ui\/jquery.ui.tabs.css":1},"js":{"misc\/ui\/jquery.ui.tabs.min.js":1,"sites\/all\/modules\/custom\/display_catalog_searches\/display_catalog_searches.js":1}},"user_alert":{"url_prefix":""},"display_catalog_searches":{"search_type":"catalogsearch","formName":"form3"},"clientsideValidation":{"forms":{"ctools-block-content-type-edit-form--2":{"errorPlacement":1,"general":{"errorClass":"error","wrapper":"li","validateTabs":"","scrollTo":1,"scrollSpeed":1000,"disableHtml5Validation":1,"validateOnBlur":1,"validateOnBlurAlways":0,"validateOnKeyUp":1,"validateOnSubmit":1,"showMessages":0,"errorElement":"label"},"rules":{"override_title_text":{"maxlength":128,"messages":{"maxlength":"override_title_text field has to have maximum 128 values."}}}},"ctools-block-content-type-edit-form":{"errorPlacement":1,"general":{"errorClass":"error","wrapper":"li","validateTabs":"","scrollTo":1,"scrollSpeed":1000,"disableHtml5Validation":1,"validateOnBlur":1,"validateOnBlurAlways":0,"validateOnKeyUp":1,"validateOnSubmit":1,"showMessages":0,"errorElement":"label"},"rules":{"override_title_text":{"maxlength":128,"messages":{"maxlength":"override_title_text field has to have maximum 128 values."}}}},"catalog-search-form":{"errorPlacement":1,"general":{"errorClass":"error","wrapper":"li","validateTabs":"","scrollTo":1,"scro…
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OK   
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HELP! What do I do?