Error Uploading Media (New Favicon)

Hello:

I’m trying to update the favicon on our site, but every time I try to upload new media, I get this message in response:

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Warning: imagecreatefromstring() [function.imagecreatefromstring]: Empty string or invalid image in /home/stephenw/public_html/hutzelmedia.com/wp-includes/media.php on line 258

Warning: imagecreatefromstring() [function.imagecreatefromstring]: Empty string or invalid image in /home/stephenw/public_html/hutzelmedia.com/wp-includes/media.php on line 258

Warning: Cannot modify header information – headers already sent by (output started at /home/stephenw/public_html/hutzelmedia.com/wp-includes/media.php:258) in /home/stephenw/public_html/hutzelmedia.com/wp-includes/pluggable.php on line 881

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Not being familiar with the technical side of setting up/editing websites, can someone help me to understand what this means. And more importantly, how to remedy the issue?

Thanks