If by "system console" you mean a local display physically connected to the machine running ENVI and "standard gnome -terminal" meaning your are attempting to launch ENVI over a remote display and connecting using ssh, perhaps the following help article can help:
http://www.exelisvis.com/Support/Help...
Regarding the cannot convert string error, I think that's just an innocuous warning because you don't have that particular font installed on the system. In which case, a different replacement system font is used by ENVI.