Grails installation fails

I'm trying to add Grails extension to STS.
However when I try to find extensions at Help->Dashboard->Extensions tab I get this error:

Some sites could not be found. See the error log for more detail.
Unable to read repository at http://www.springsource.com/milestone/e3.4/site.xml.
Server returned HTTP response code: 403 for URL: http://dist.springsource.com/milesto.../e3.4/site.xml
Unable to read repository at http://www.springsource.com/snapshot/e3.4/site.xml.
Server returned HTTP response code: 403 for URL: http://dist.springsource.com/snapsho.../e3.4/site.xml

Can I somehow downoad the extension and install it manually?

It would be better to post this in the SpringSource Tool Suite forum. I'm afraid I don't know if it's possible to get hold of the extension separately. That said, you seem to be using an old version of STS if it's checking for e3.4. The latest STS is based on Eclipse 3.7. I think there are update sites for e3.6 and e3.7 as well, but not sure about e3.4.

Cannot complete the install because one or more required items could not be found.
Software being installed: Groovy-Eclipse Feature 2.5.2.xx-20110729-1800-e37

I hit the groovy-eclipse dependency once or twice before, but I have the snapshot as an update site to get the latest and greatest. Usually when I install a new STS, I start with Groovy Eclipse first, let that install, then layer on Grails and other things under the extension tab. Also, it might help if you try to install via the Spring dashboard/extension tab, as opposed to manually adding the update sites.

Last but not least, the 2.7.1/2.8.0M1 are vastly improved compared to the 2.5 or earlier versions of STS, so it is well worth the upgrade.