Problem solving - display of grouped products page - Magento

I've got a live webshop using Magento 1.5.1. and I've always been working with simple products. Now that I decided to use also grouped products I get an error if I open a grouped product page. Probably due to an extension conflict, but I need some one to take a look at this for me. I only know the basics. I have several extensions installed. I'd like to find some one who can have this solved even today so that I can start working on monday without any issues.