Here is the error:

Fatal error: Call to a member function get_id() on a non-object in /path/to/lib/blocklib.php on line 920

Here is the traceback:

• line 919 of lib/blocklib.php: call to debugging()
• line 453 of lib/blocklib.php: call to blocks_get_by_page()
• line 2710 of lib/adminlib.php: call to blocks_setup()
• line 47 of files/index.php: call to admin_externalpage_print_footer()
• line 616 of files/index.php: call to html_footer()

To reproduce:

1. On the site home page, add a resource that links to a file or web page.
2. Click on the Choose or upload a file... button
3. Error is displayed at the bottom.

I haven't tested to see if this is still a problem in 1.9 or later, but the code is different post 1.8 due to MDL-9647