I spend quite a bit of time on the Squarespace Developer Forums (which is somewhere I highly recommend if you need help) and the most common problem I see when people are adding new custom scripts or features is incorrect references to external files!
Many of you will be familiar with going into File Storage to upload new files and if you are used to using the WYSIWYG (what you see is what you get) editor to insert/link files, you won’t have needed to know how to reference files in manually. Any files you upload into File Storage can be linked to by adding “/storage/” and then the pathname to the file you see in File Storage.
For example, if you see a folder called “photos” with the file “image1.jpg” inside, to link to it you would use “/storage/photos/image1.jpg”.
Note: One error I have seen is to omit the forward slash before storage, this can cause confusion because it will work on your home page, but not any other page. This is because if you omit the slash, the link becomes relative from the current url (e.g. yourdomain.com/gallery/) not the base url (e.g. yourdomain.com).
To solve this you need to edit the CSS file and fix the link. An example is a file linking to multiple background images in the format of “/images/bg.png”. This obviously won’t work on Squarespace as www.yourdomain.com/images/ doesn’t exist (as a file storage directory). My approach is to open up the file in a text editor and find/replace, “/images” with “/storage/images” (assuming that is correct for however you uploaded them!). Re-upload the file and all should be well. (Beware of uploading files of the same name again, as Squarespace or your browser might cache them and take a while to update).
How to tell if you have broken links:
Get your browser to check! Bring up the developer/error console in your browser (they differ from browser to browser) and look at what it says. I use chrome for development and the picture below is what you would see if you have a broken link:
How to open the developer console:
Chrome (Mac): Alt+Cmd+J
FF (Mac): Cmd+Shift+J
Chrome/FF (Windows): Ctrl+Shift+J
(I can’t really recommend doing primary web development in any other browsers as of 2012)