Login Problem

Hi

I purchased a blog solution, and the developer is now unwilling to assist with this matter. please can someone help, as my knowledge is very limited with regard to the technical aspects that are being presented.

The site seems to be running fine, but when I login to the admin area, on the login screen I get the following message above the login details ‘box’

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-login.php on line 255

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-login.php on line 267

And then after logging in there is no dashboard but only a similar message, which states

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-login.php on line 255

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-login.php on line 267

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-includes/pluggable.php on line 649

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-includes/pluggable.php on line 650

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-includes/pluggable.php on line 651

Warning: Cannot modify header information – headers already sent by (output started at /home/green/public_html/wp-content/plugins/all-in-one-seo-pack/all_in_one_seo_pack.php:4157) in /home/green/public_html/wp-includes/pluggable.php on line 850

From there I cannot go any further?

Please can someone help, considering the original developer, or person responsible is not willing to help me.

Thanks
Andre