The error seems to be that your site does not have access to the web.config file. First, check to be sure there is a config file there. Next, check what the permissions are set to on the file. The process that runs your app pool should have access to read the web.config file. Here is a Stack Overflow question with more details:
http://stackoverflow.com/questions/5615296/cannot-read-configuration-file-due-to-insufficient-permissions[
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Since this is a hosted environment, there may be some things that are outside your control (shouldn't be, but I've seen it happen). If that is the case, you will need to contact your hosting company for help. However, don't do that until after you have walked through the above solutions and tried them.