I use GDE 2.2 on Linux (Debian Potato), it works on my machine without bigger
problems. I also integrated several external programs (tacg, primer3, clustalx,
Jalview, etc) into the GDE menus.
(The EMBOSS package is much more versatile and uptodate, but sometimes I still
preferr GDE, because of the nice user interface.)
The reason of problem with opening files may be e.g. that you do not have /tmp
subdirectory in the directory, were you have GDE installed.
Note also, that GDE can open only GDE and GenBank format files. For other
formats you should use the "Import Foreign Format" option.