I have more then once been bitten by that fact that in lists the hyperlink column has a limitation on the length the URL can be. This has become an issue specifically with URLs for document libraries.
You will find that the URL for a document library and specifically to a folder within the document library is ugly. You can see this with this example:
OK, you can see that the URL essentially is duplicated within itself. Now this just makes the URL long and can affect using it in another list that has a column for hyperlinks. There is a solution to this:
Looking at the URL you will only need the first third (up to the document library name) and then add the folder name after. So let's use the URL above as an example:
Step 1: Cut to the end of the document library name.
Step 2: Add the folder name you want to link to. You can do sub folders too. Also make sure if there is a space in the folder name to add the following as your space: %20
Example 1: to a folder called Communication at the root level
Example 2: to a sub folder under Communications called Letters
You URL now is very manageable, much easier to review and know where it will take you.