[Lazarus] "Can not find <package unit> used by Lazarus"

[Kenneth Cochran]

Using Lazarus 1.0.10 on Windows 7 64-bit. The IDE appears to be running as
a 32-bit application in case that makes a difference.

I am working on my first package and it compiles fine but whenever I
attempt to install it using either the "Installed Packages" or "Package
Editor" dialogs I get the following message

PPU Loading ..\ideextensions\lib\i386-win32\ideextensions.ppu
PPU Source: ideextensions.pas not found
Recompiling ideextensions, checksum changed for ide
(1,1) Fatal: Can not find ideextensions used by Lazarus,
ppu=..\ideextensions\lib\i386-win32\ideextensions.ppu, package ideextensions

I shortened the path to '..' for brevity's sake. The actual path in the
error message is a subfolder in my Windows user profile. The unit it's
looking for (ideextensions.pas) appears to be created and maintained by the
IDE whenever you add or remove dependencies using the package editor. I am
certain it exists exactly where the IDE put it.

This is a brand new package with all package options set at the default.
What could be causing this? Can anyone else reproduce this behavior?
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