To expand on the previous post, because it is unconditional, your Redirect will also be invoked for the redirected request, leading to a loop:
1st request: /somefile -> redirects to /folder/somefile 2nd request: /folder/somefile -> redirects to /folder/folder/somefile 3rd request: /folder/folder/somefile -> redirects to /folder/folder/folder/somefile
etc. This continues until the maximum redirection limit for either the browser or the server is reached, whichever is lower.
If you have sufficient permissions from your host to use mod_rewrite [httpd.apache.org] in .htaccess, then you can test the requested folder, and only redirect if "/folder" is not present in the request. This will prevent the looping. Something like: