MyBB Hacks

Thank you in advance if you can help me solve this one!

I am admittedly a newbie - I just installed MyBB today. I am having trouble installing XThreads. Once I extracted the files, I dragged folders under "Upload" into my root folder (public_html), and they seem to have sorted into the appropriate folders.

Based on my searches here, I have checked "class_page.php" for extra spaces on line 151 and did a find replace in "xthreads_attach.php" for require and replaced with require_once, neither did anything.

When I go into Configuration > Plugins I get the following wall of text:

Warning [2] Cannot modify header information - headers already sent by (output started at /home/username/public_html/admin/inc/class_page.php:151) - Line: 24 - File: inc/plugins/xthreads_attach.php PHP 5.6.31 (Linux)

File Line Function
[PHP] errorHandler->error
/inc/plugins/xthreads_attach.php 24 header
/inc/plugins/xthreads_attach.php 96 fatal_error
/inc/plugins/xthreads_attach.php 382 do_processing
/admin/modules/config/plugins.php 518 require_once
/admin/index.php 821 require

Warning [2] Cannot modify header information - headers already sent by (output started at /home/username/public_html/admin/inc/class_page.php:151) - Line: 25 - File: inc/plugins/xthreads_attach.php PHP 5.6.31 (Linux)

File Line Function
[PHP] errorHandler->error
/inc/plugins/xthreads_attach.php 25 header
/inc/plugins/xthreads_attach.php 96 fatal_error
/inc/plugins/xthreads_attach.php 382 do_processing
/admin/modules/config/plugins.php 518 require_once
/admin/index.php 821 require
Can't find XThreads base directory.

It doesn't look like files were uploaded into to the correct directories.  You'll need to delete all the XThreads files you uploaded then upload them into the correct location.  What's in Upload needs to end up in the root, not inside inc/plugins.