shift cable question

[jwclbi]

I have a 225 merc, recently removed engine, rebuilt transom and reinstalled engine. the shift cable and throttle cable were obviously removed by taking the nuts off and simply put them back on exactly the way they came off. Now when I shift into gear every now again it is very very difficult to get into gear, or back to neutral. When the cable is off the engine linkage its easy and smooth. I can shift the engine linkage with my fingers with ease as well. any thoughts? thanks