It can be frustrating very much so... but things mentioned above are all relevant... i will add that the position you are viewing from very much determines whether it will place or (in most cases) not ..ie if you cannot "see" the bottom of something digging a hole may help. or try and "see" the surface you wish to connect to .if you cant see it, it pretty much wont lock. i have just finished a huge round building with stone floors on two levels and realised the very bottom foundations were not ALL blue tinted well one wasnt..... which was the same area where everything was breaking two floors up!..so check out links on building heights and similar if your plans are big ones! oh edit: if you build a platform you have to "see" the leading edge..which can be dangerous if platform is high..of course!