I don't know how you have done the installation, but you just need to unzip the file in your \3d Rad folder and start radimp.exe
So check :
1. Is 3d Rad installed ?
2. RadImp_v0.9.zip unzipped into you 3d Rad folder and no subfolders of 3drad ?
3. Is 3Drad.exe and Radimp.exe in the same folder ?
So check :
1. Is 3d Rad installed ?
2. RadImp_v0.9.zip unzipped into you 3d Rad folder and no subfolders of 3drad ?
3. Is 3Drad.exe and Radimp.exe in the same folder ?