While I normally work with Laz/main+FPC-3.2.2, I now compiled and installed the ExCtrls packages with Laz 2.2.4+fpc3.2.2, both on Windows. No problem.
Nicole, what are you doing? Which Laz version? Which OS?
When such strange errors happen it is usually best to try a clean rebuild of the IDE with the new package. At first delete the lazarus.exe which failed to build. Make a copy of lazarus.old.exe and rename the copy to lazarus.exe -- now you have the IDE back from which you started all this. You must repeat the steps for the installation, but now do some more intermediate steps:
Go to "Package" > "Open package file" and load ExCtrlsPkg.lpk. Then load the design package ExtCtrlsPkg_Design.lpk, click "Use" > "Install", but do not allow to rebuild the IDE. Rather than that, exit the package editor and go to "Tools" > "Configure Build Lazarus": in the "Cleanup" box check "Clean all" and "Switch after building to automatically". "Build" starts the compilation which takes a bit longer now and should be successful.