Sometimes you don't really learn some of the most important words in classic language lessons. I'm not saying language lessons aren't useful: far from it! It's just some essential terms slip under the net. Very often these are expressions or sayings that you just don't learn, you pick up.
For example 'attached'. This, in the sense of 'please find the document attached (to an email)'. And here the problem starts. You don't know what attached is, so you look it up in a dictionary which just says something like, 'aangesloten' (more like connected), so you use it! Unfortunately it seems that this is not the correct word to use.
Fortunately for me, my Dutch speaking friends are cool and have informed me that:
"ingesloten" of "in bijlage" is the norm.
Keep making mistakes everybody! But always be ready to accept corrections. It's the only way to improve.