Using mgos 2.01 (and the FF 3 patches) and I can reproduce the problem it using the basic viewer on Opera, there is no error reported in the Opera Console
testing with fiddler, the last successful request is
OPERATION=GETVISIBLEMAPEXTENT&VERSION=1.0.0&SESSION=ed3b85bc-ffff-ffff-8000-00163e654f42_en_7F0000010AFC0AFB0AFA&MAPNAME=Sheboygan&SEQ=0.1061965599656105&SETDISPLAYDPI=96&SETDISPLAYWIDTH=1223&SETDISPLAYHEIGHT=793&SETVIEWSCALE=56304.15451497935&SETVIEWCENTERX=-87.7302542509315&SETVIEWCENTERY=43.744459064634&CLIENTAGENT=Ajax%20Viewer
which returns some xml bounds
the next request (which never is made by opera) using Firefox is
GET /mapguide/mapagent/mapagent.fcgi?OPERATION=GETDYNAMICMAPOVERLAYIMAGE&FORMAT=PNG&VERSION=1.0.0&SESSION=bcfbe93c-ffff-ffff-8000-00163e654f42_en_7F0000010AFC0AFB0AFA&MAPNAME=Sheboygan&SEQ=0.34199134868538994&CLIENTAGENT=Ajax%20Viewer