Can't create new DLL?

[General Fear]

I am using VB.Net 2010.
I am creating my own custom controls. I moved the old custom control DLL to another directory. I created a new DLL and copied it to the directory where the application resides thus replacing what was there. When I fire up the application I get an error that says " 'My_Common_Control_Library' is not declared. It may be inaccessible due to its protection level."
What is going on?

 

[Don Delegate]

Did you remove the reference to the old assembly from your project and did you add a reference to the new assembly in your project?

 

[jmcilhinney]

Did you change the interface (API, not UI) of that library? Did you change the version number of that library?

 

[General Fear]

Did you change the interface (API, not UI) of that library? Did you change the version number of that library?

Don wrote:
"Did you remove the reference to the old assembly from your project and did you add a reference to the new assembly in your project? "

No I did not. I thought that if a drop a dll and ad a new dll, even if it is the same name, that the controls on the form would go away and I would be forced to place them again on the form.

jmcilhinney wrote:
"Did you change the interface (API, not UI) of that library? Did you change the version number of that library?"

I did change my DLL. I wanted to programmatically change the background color of the textbox. The goal was, if it is a required textbox, make the background yellow. I created a new DLL and copied it to the directory were the old DLL was. Then I got the above error message.