If seamless wont open anymore but use to, go to the folder:
My Documents\Seamless3d\Application Data For Seamless3d
and delete the seamless3dSetup.wrl file.
My Documents\Seamless3d\Application Data For Seamless3d\Recover
In here there will be all the smls files that get backed up after each command.
The incremental numbers for the filenames and the date of the file can help to figure which file was what.
Help is always on hand at the forum. Seamless3d specific questions are much valued but please use the forum rather than posting emails directly to me if possible because questions on the forum help to keep the forum alive and so your questions will in turn help this free open software flourish. Please don't feel concerned about asking silly questions, the forum is there to help. If there is any point in a tutorial where you are unsure or would like to understand something better, ask away.