Can't give a dimension to several holes in sketch

Hi,

I'm a student using Solidworks 2012-2013. I'm making simple sketches of 4 parts of a flute, and I having problems giving dimensions.

I have several holes and arcs, and I keep getting this message "The selected entity could not be converted into a line or a circular arc",

or "The selected silhouette cannot be uniquely identified for the current operations. Please create a split line by using Split Line operation with the silhouette option."

I already saw whis similar message https://forum.solidworks.com/message/235657.

Problem is, he treats the sketch like it's fully-defined so I can't use those tricks of showing hidden axes and stuff. Also, I didn't understand some of the advices you gave that guy. For example, if I sketch a centerline, then give the dimension to the centerline- the centerline stays, I can't hide it.. so it's noticeable that I gave the dimension to the line, not to the hole...

I'm attaching a picture of the sketch. Maybe you could help.

Thank you!

SolidworksSketching