PEAR webinstaller

Why can some PEAR packages not be installed ?

For example. I click on "show not installed". Then all the packages that are
 not installed are listed.
Lets take the first one. Unter "caching"the is the package APC.

Its say nothing on local and latest 2.0.4.

In the package management option it says "not installed."
I click on "install package" and the error " Package name " not valid".

Same with tons of other packages.
Is there something misconfigured ? I installed lots of other packages withou
t any problems.

Thank you very much.