Fatal error: Cannot redeclare class GeSHi in /homepages

Immediately after trying to delete a plugin, this error message appeared on my screen – ‘
Fatal error: Cannot redeclare class GeSHi in /homepages/18/d109823931/htdocs/sharon-Backup/taste/wp-content/plugins/igsyntax-hiliter/geshi.php on line 259′. The plugin that I was trying to delete is ‘igsyntax-hiliter’as far as i know.

It seems to have affected these pages primarily;-‘http://www.sharons.org.uk/wp-admin/plugin-install.php
http://www.sharons.org.uk/wp-admin/plugins.php
http://www.sharons.org.uk/wp-admin/options-general.php?page=updraftplus’

From a googling research it appears to be a known bug with ‘geshi’ but no solution that I saw.

How do I regain control of my blog please?

Thanks
Sharon.