Jim,

I am not sure what the exact problem is, but I know that the webserver assigns an ID attribute to all server controls on your page if you don't, and their name is usually a string that contains a "__ctrl" substring.

I made a custom control that dynamically instantiated and loaded subcontrols and got an error message that I fixed by creating a static integer ID field in my class, that I incremented in my class constructors,

public class CustomControl
{
static int ccCount;
...

public CustomControl ()
{
ccCount++;
...

and manually assigning an ID to every control that I added dynamically in my method, i.e.,

CustomControl aControl = new CustomControl();
aControl.ID = "control" + CustomControl.ccCount;

to circumvent the webservers automatic assignment.

Microsoft has a hotfix that we had to contact them to download, and it didn't fix the problem, but we had two levels of dynamic creation, i.e., we loaded a control that dynamically created controls that dynamically created controls. Even if you aren't dynamically creating controls, you might try assigning ID attributes to all the server controls that you have. I think Microsoft automatic ID assignment is wonky.