Shattered Kingdoms

I type .c to clear or .f to format and i get the message: "%%% Invalid character in speedwalk string: c" or "%%% Invalid character in speedwalk string: f"

That speed walk string bit makes it sound like the issue is a conflict with your client.
I was trying to get my client to do something recently, and made it so I could no longer use ";" to talk to the group.
Unfortunately I don't know much about clients, so while I was able to fix my issue, I have no idea what's causing yours. But I definitely think its a client issue rather than an in game bug.

I'm not sure what client you have, but I'm going to go ahead and guess Zmud, because I had similar confusion when I first started using it. If this is the case, it's an easy fix:

In your toolbar, go to View > Preferences > Special Characters > and then uncheck the box for " Movement Char . "

If you use zmud click on that little computer in the right hand bottom of the window to quickly turn off parsing so you can use .f .c and .s