dll - C# using <myowndll>, doesn't work (VS10 Express) -

background: novice in c#, , use visual studios 2010 express.

i have class (let's call myclass) want use in multiple projects. used add classes project->add existing item... creates copy of myclass.cs.

now found out when build original myclass.cs creates myclass.dll , places in release folder of project.

but when try use dll, following error:

the type or namespace name 'myclass' not found(are missing using directive or assembly refference?

which weird me, because i have referenced it (it in reference folder of solution explorer). , have added code:

using myclass; 

so doing wrong?

update: when tried old method (add existing item -> myclass.cs) error message goes away. it's not matter of spelling things correctly.

add dll first:

click on references in project-explorer in visual studio , add dll can use expected it.