Why is Eclipse not letting me install new updates? - eclipse

Question

I’m using the following version of Eclipse on Mac 10.9.5
Eclipse Java EE IDE for Web Developers.
Version: Juno Service Release 2
Build id: 20130225-0426
When I click on “Help” -> “Check for Updates”, I get the “Available Updates” dialog
The operation cannot be completed. See the details.
Cannot complete the install because one or more required items could not be found.
and there is only a “Cancel” dialog. When I click “Cancel,” a smaller dialog appears with the message
Some sites could not be found. See the error log for more detail.
and when I click the “Details” button, I get
Some sites could not be found. See the error log for more detail.
No repository found at http://download.eclipse.org/mat/1.3.1/update-site/.
Unable to read repository at jar:file:/Users/davea/Downloads/ehep-1.0.0.zip!/site.xml.
error in opening zip file
At this point, I don’t know what else I need to do to successfully install updates or correct the existing problem.
Edit: Following the suggestion, I fixed the broken repositories, however, now when I get the Available Sites dialog, I only check the
Eclipse IDE for Java EE Developers
option, yet I still get these errors, complaining about conflicting dependencies. How do I get around these?
Cannot complete the install because of a conflicting dependency.
Software being installed: Eclipse IDE for Java EE Developers 2.0.2.20140224-0000 (epp.package.jee 2.0.2.20140224-0000)
Software currently installed: m2e - Maven Integration for Eclipse 1.3.1.20130219-1424 (org.eclipse.m2e.feature.feature.group 1.3.1.20130219-1424)
Only one of the following can be installed at once:
Maven Integration for Eclipse 1.5.1.20150109-1820 (org.eclipse.m2e.core 1.5.1.20150109-1820)
Maven Integration for Eclipse 1.4.0.20130601-0317 (org.eclipse.m2e.core 1.4.0.20130601-0317)
Maven Integration for Eclipse 1.5.0.20140606-0033 (org.eclipse.m2e.core 1.5.0.20140606-0033)
Maven Integration for Eclipse 1.5.2.20150413-2215 (org.eclipse.m2e.core 1.5.2.20150413-2215)
Maven Integration for Eclipse 1.2.0.20120903-1050 (org.eclipse.m2e.core 1.2.0.20120903-1050)
Maven Integration for Eclipse 1.1.0.20120530-0009 (org.eclipse.m2e.core 1.1.0.20120530-0009)
Maven Integration for Eclipse 1.4.1.20140328-1905 (org.eclipse.m2e.core 1.4.1.20140328-1905)
Maven Integration for Eclipse 1.3.0.20130129-0926 (org.eclipse.m2e.core 1.3.0.20130129-0926)
Maven Integration for Eclipse 1.3.1.20130219-1424 (org.eclipse.m2e.core 1.3.1.20130219-1424)
Cannot satisfy dependency:
From: Eclipse IDE for Java EE Developers 2.0.2.20140224-0000 (epp.package.jee 2.0.2.20140224-0000)
To: org.eclipse.epp.package.jee.feature.feature.group [2.0.2.20140224-0000]
Cannot satisfy dependency:
From: Java EE IDE Feature 2.0.2.20140224-0000 (org.eclipse.epp.package.jee.feature.feature.group 2.0.2.20140224-0000)
To: org.eclipse.m2e.wtp.jpa.feature.feature.group 0.0.0
Cannot satisfy dependency:
From: m2e - Maven Integration for Eclipse 1.3.1.20130219-1424 (org.eclipse.m2e.feature.feature.group 1.3.1.20130219-1424)
To: org.eclipse.m2e.core [1.3.1.20130219-1424]
Cannot satisfy dependency:
From: Maven Integration for Eclipse WTP 1.0.0.20130612-1742 (org.eclipse.m2e.wtp 1.0.0.20130612-1742)
To: bundle org.eclipse.m2e.core [1.4.0,2.0.0)
Cannot satisfy dependency:
From: Maven Integration for Eclipse WTP 1.0.0.20130613-0136 (org.eclipse.m2e.wtp 1.0.0.20130613-0136)
To: bundle org.eclipse.m2e.core [1.4.0,2.0.0)
Cannot satisfy dependency:
From: Maven Integration for Eclipse WTP 1.0.1.20130911-1545 (org.eclipse.m2e.wtp 1.0.1.20130911-1545)
To: bundle org.eclipse.m2e.core [1.4.0,2.0.0)
Cannot satisfy dependency:
From: Maven JPA Configurator 1.0.0.e42-20130613-0136 (org.eclipse.m2e.wtp.jpa 1.0.0.e42-20130613-0136)
To: bundle org.eclipse.m2e.wtp 1.0.0
Cannot satisfy dependency:
From: Maven JPA Configurator 1.0.0.e43-20130612-1744 (org.eclipse.m2e.wtp.jpa 1.0.0.e43-20130612-1744)
To: bundle org.eclipse.m2e.wtp 1.0.0
Cannot satisfy dependency:
From: Maven JPA Configurator 1.0.1.e42-20130821-1033 (org.eclipse.m2e.wtp.jpa 1.0.1.e42-20130821-1033)
To: bundle org.eclipse.m2e.wtp 1.0.0
Cannot satisfy dependency:
From: Maven JPA Configurator 1.0.1.e43-20130911-1546 (org.eclipse.m2e.wtp.jpa 1.0.1.e43-20130911-1546)
To: bundle org.eclipse.m2e.wtp 1.0.0
Cannot satisfy dependency:
From: m2e-wtp - JPA configurator for WTP (Optional) 1.0.0.e42-20130613-0136 (org.eclipse.m2e.wtp.jpa.feature.feature.group 1.0.0.e42-20130613-0136)
To: org.eclipse.m2e.wtp.jpa [1.0.0.e42-20130613-0136]
Cannot satisfy dependency:
From: m2e-wtp - JPA configurator for WTP (Optional) 1.0.0.e43-20130612-1744 (org.eclipse.m2e.wtp.jpa.feature.feature.group 1.0.0.e43-20130612-1744)
To: org.eclipse.m2e.wtp.jpa [1.0.0.e43-20130612-1744]
Cannot satisfy dependency:
From: m2e-wtp - JPA configurator for WTP (Optional) 1.0.1.e42-20130821-1033 (org.eclipse.m2e.wtp.jpa.feature.feature.group 1.0.1.e42-20130821-1033)
To: org.eclipse.m2e.wtp.jpa [1.0.1.e42-20130821-1033]
Cannot satisfy dependency:
From: m2e-wtp - JPA configurator for WTP (Optional) 1.0.1.e43-20130911-1546 (org.eclipse.m2e.wtp.jpa.feature.feature.group 1.0.1.e43-20130911-1546)
To: org.eclipse.m2e.wtp.jpa [1.0.1.e43-20130911-1546]

Answer 1

When you open http://download.eclipse.org/mat/1.3.1/update-site/ in a browser, it says that it moved to http://archive.eclipse.org/mat/1.3.1/update-site/. Maybe you can try this.
I haven't tried this, but it seems like you can configure the Update Site location using Window -> Preferences -> Install/Update -> Available Software Sites, and there finding and replacing the above location.
About that other error: Seems like you added some local archive site some time ago and since then deleted or moved that archive. If you still need it, try to restore it, otherwise use the above preferences to remove it.
Having said that, it might be a good idea to move on to a newer version of Eclipse...