Common problem. Caused by the fact that UFT operates in a Windows 3.1 environment, which supports a maximum of 250-300 fonts at one time. (Win95 supports up to 1000). First, verify that Roots Font is still on your computer, and then transfer some of your other unused fonts to a different directory.
From UFT Knowledge Base: "The ROOTS font is used for lines and spacing in selected reports. If the ROOTS font is missing from the Fonts window, strange characters or will appear in reports.