Problem with plugins(no permission to access)

Hello,

I hope someone can help me with the following problem:

I have got some plugins installed which you can use in the Wysiwyg editor when you edit a page. Only when I click on one of the plugin icons I get the following error message:

Forbidden

You don’t have permission to access /wp-content/plugins/boxer/framework/admin/blocks.php?ver=359-20131026 on this server.

I have tried finding a solution on google but couldnt find one. Does anyone know where the problem comes from and how to fix it? Thanks in advance.

Sjoerd