Are you using Ubuntu, under a network which has a proxy configured?
And, after installing the Subclipse Eclipse plugin you are getting the “RA layer request failed” error?

Configuring proxy by entering the address and port number in Eclipse preferences will not solve this.

Proceed with the following:

1. $ cd ~/.subversion/
2. $ vim servers
3. In the servers file, find the lines with http-proxy-host and http-proxy-port under [global] section.
4. Uncomment those lines and enter the host address and the port number respectively for http-proxy-host and http-proxy-port.
5. Save and close the editor.
6. In the SVN Repository view in Eclipse, try adding a new repository location.

Note: Make sure you don’t leave a space before the statements after uncommenting the two lines as said above, else you are likely to get the error Cannot map the project with svn provider.

ps: tested using Ubuntu 10.04; SVN interface: JavaHL (JNI) 1.6.6

sudo  apt-get install libsvn-java, to install the JavaHL interface.

The default installation dir is: /usr/lib/jni

If Eclipse do not pick automatically this directory, add the following line to your eclipse.ini, as a argument bellow of “-vmargs”:

-Djava.library.path=/usr/lib/jni

sorces:

http://varshamyspace.blogspot.com/2010/08/setting-up-proxy-for-subclipse-in.html

http://islandlinux.org/howto/installing-javahl-subclipseeclipse-ubuntu

Exemplo:

Alguns plugins como o m2eclipse necessitam que o Eclipse execute utilizando a JDK e não a JRE:

The Maven Integration requires that Eclipse be running in a JDK, beacuase a number of Maven core plugins are using jars from the JDK.

Please make sure the -vm options in eclipse.ini is pointing to a JDK and verify that Installed JREs are also using JDK installs.