Actually it should work unless these two db files are from different vendors and they are very different...in this case your 180nm db file will be included in link library and your target library will be declared as 90nm db...
do you have other library files? if yes then you must be having the symbol library as well. you just have to figure it out. i can provide you with the file but that wont work for real fabrication purposes. you can use that file for simulation and understanding the tool though.