Anopinion wrote:

sorry but this is actually the first time you heard of this???

He is refering to the fact if anything so much as a pebble is between you and your target and you try to cast on the target, you get the "you cannot see your target" bs.

Pets and other things effect this also i believe.
Of course I'm aware of the issues with our collision system and line of sight, but I wasn't sure there wasn't some other issue the original poster was referring to. Also, the logic is akin to "if you don't wash my car, I'm not going to bother driving to work."