It happened once to me when I was using VS 2003. After wasting a day
trying numerous things, I believe that the fix was to remove and add
back the reference to the web project.

It's not much to go on but I hope that helps.

Regards.

I have had this problem several times in VS.NET 2005.

A lot of the time I just do a Clean and Rebuild (not a build) and they
will show back up.  I don't have VS.NET 2005 here so the actual
verbiage may be off a little.

However, there have been times when something "minor" was wrong in the
code and they would not show up.  Minor being that it's apparently not
important enough for them to show it in the Error or Warnings list.
Once I figure out what wrong it show back up, make sure to Clean and
Rebuild each time.  Also keep in mind if they are all in the same
assembly it is an all or nothing thing so start the last control you
edited.

I hope this helps.

-Wayne