I had a heck of a time with the Try It Out beginning on page 158 dealing with collections. I figured out my problem and wanted to share my experience in case someone was having the same difficulty.

When I created the "CustomerCollection" class and entered all of the code, I went down the page and entered everything as it appears. This generated an error on both steps 3 and 4 regarding a namespace issue.

It is not clear from the book (at least not to me) that the code from steps 3 & 4 need to come before the "End Class" statement from step 2. Once I rearranged my code this sorted everything out.