Losing package references between opening/closing project

Hi folks,

I'm new to the world of Unity (tho experienced in C/C++/OpenGL), and I just got myself Unity Pro, NGUI, and the ProtoPack from http://www.frogames.net/content-packs/protopack.html . I've run into a stressful problem in my workflow. I'm sure I must be missing something obvious, but wanted to run it by you:

1) Create new project (no additional packages checked off)

2) Right-click in Project Window to Import Package

3) Load in NGUI (from the shared folder where asset store downloads go)

4) Do the same thing for ProtoPack, except from the folder where I extracted the .zip file containing the .unityPackage file (since I did not buy it from Asset Store)

5) NGUI appears in the menu at the top (I assume "Import Package" was successful!), and ProtoPack options appear in Components menu (I assume "Import Package" was successful as well).

6). Save & close project

7) Re-open : ERROR ---> compiler errors for unknown identifiers in ProtoPack script, and NGUI menus are no longer present at the top. Re-importing from scratch again seems to have no affect.

Any ideas how I can maintain the correct state of packages in between opening and closing the same project?

Thanks a bunch