I have had this same problem occur before, and while I am not sure what caused it, I can tell you that I was able to fix it by logging into my machine as an admin, deleting my user profile, then logging back into the machine as with my regular account thus having it recreated. This assumes you are using a Windows machine that is one an Active Directory controlled domain. Also, be sure to back anything important in your profile up prior to trying this.
Dave G.
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