Hi, may I ask what theme you are using in your webshop? We have seen cases where the theme is not coded properly so it need a fix. Many theme developer has allready made fixes to this. Also you can try as a temporary solution to turn of magento swatches, to see if the theme swatch will then work.
Can you please provide us with some more information. Like does the /var/log/system.log or exception.log says have any information? Do you have a php error log in the root folder etc. called error_log that is giving errors?