Q1 - When you created your project, did you choose Excel 2003 Add-in from the list of Visual Studio Installed Templates?
If not, there's your reason.
Q2 - If you did, do you have a file called ThisAddIn.cs with the line publicpartialclassThisAddIn?
Q3 - If you right-click on ThisAddIn and choose Go toDefinition, do you get offered 2 choices - the second being in a file ThisAddIn.Designer.cs?
If you click on that choice and thereby open the file, check the following.
(a) Q4 - Is the namespace in that file the same as that in your file referencing Globals.Application.ActiveWorkbook?
(b) Q5 - In that file, is there a line internalsealedpartialclassGlobals {?
The answers to all 5 questions should be yes but in that case you wouldn't get the error you report.
Any No answers should help you identify the problem.