Created attachment 79197 [details]
stacktrace

Build: NetBeans IDE Dev (Build 200903250219)
VM: Java HotSpot(TM) Client VM, 11.2-b01, Java(TM) SE Runtime Environment, 1.6.0_12-b04
OS: Windows XP, 5.1, x86

User Comments: 
insatalling http://blogs.sun.com/netbeansphp/resource/other/org-netbeans-modules-php-prado-001.nbm

Stacktrace: 
java.util.concurrent.ExecutionException: java.lang.AssertionError: C:\Documents and Settings\Paul A Norman\.netbeans\dev\update\download\org-netbeans-modules-php-prado.nbm
        at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:0)
        at java.util.concurrent.FutureTask.get(FutureTask.java:0)
        at org.netbeans.modules.autoupdate.services.InstallSupportImpl.doValidate(InstallSupportImpl.java:253)
        at org.netbeans.api.autoupdate.InstallSupport.doValidate(InstallSupport.java:110)
        at org.netbeans.modules.autoupdate.ui.wizards.InstallStep.handleValidation(InstallStep.java:407)
        at org.netbeans.modules.autoupdate.ui.wizards.InstallStep.doDownloadAndVerificationAndInstall(InstallStep.java:185)

Created attachment 79198 [details]
stacktrace

Build: NetBeans IDE Dev (Build 200904011705)
VM: Java HotSpot(TM) Client VM, 1.5.0_16-133, Java(TM) 2 Runtime Environment, Standard Edition, 1.5.0_16-b06-284
OS: Mac OS X, 10.5.6, i386

User Comments: 
trying to install HAML plugin in 6.7M3 oh pretty pretty please make this work. 

Stacktrace: 
java.util.concurrent.ExecutionException: java.lang.AssertionError: /Users/jdwyah/.netbeans/6.7m3/update/download/org-netbeans-modules-haml.nbm
        at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:205)
        at java.util.concurrent.FutureTask.get(FutureTask.java:80)
        at org.netbeans.modules.autoupdate.services.InstallSupportImpl.doValidate(InstallSupportImpl.java:250)
        at org.netbeans.api.autoupdate.InstallSupport.doValidate(InstallSupport.java:110)
        at org.netbeans.modules.autoupdate.ui.wizards.InstallStep.handleValidation(InstallStep.java:407)
        at org.netbeans.modules.autoupdate.ui.wizards.InstallStep.doDownloadAndVerificationAndInstall(InstallStep.java:185)

Created attachment 79293 [details]
stacktrace

almost all fails in the issue are with haml and prado plugins, just tried to install haml and all was ok.
so the issue doesn't mean this specific lugins can't be installed, but the issue may be more visible with these plugins.

On hearing that you were able to install the plugin, I gave it another shot.
I've been trying to install from http://mediacast.sun.com/users/tnorbye/media/org-netbeans-modules-haml.nbm/details  
The file is a jar, but I just changed the plugin adder to accept all files. 

Today I renamed the jar to be a .nbm and it worked.  

thanks, 
looks strange as report points to "/Users/jdwyah/.netbeans/6.7m3/update/download/org-netbeans-modules-haml.nbm"
It may means plugin manager task replace extension at some point, and fail to find appropriate file.
Do you mean  you report was done when module had "org-netbeans-modules-haml.jar" name?

was able to install prado downloaded from latest link

thanks, tried myself and was able to reproduce the issue after changing nbm extension to jar extension.
also it means there should be easy workaround for the issue.

Yeah this fails when 6.7 M3 offered to auto-update my plugins from M2 (or M1?). I can't say for sure what the plugin extension was, but it was the same 
download, so probably .jar. It worked without incident in M1&2.

I`d say that the best workaround is to ignore files (that come from file chooser) that do not have .nbm extension.

Assertion is fixed and non-nbm files are not handled, see also Issue 36858.
http://hg.netbeans.org/core-main/rev/150610c1f570

Integrated into 'main-golden', will be available in build *200904160201* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
Changeset: http://hg.netbeans.org/main-golden/rev/150610c1f570
User: Dmitry Lipin <dlipin@netbeans.org>
Log: Issue #161643 AssertionError: C:\Documents and Settings\Paul A Norman\.netbeans\dev\update\download\org-netbeans-modules-php-prado.nbm

This is a bit tangential to the actual bug here. But if anyone on the NetBeans team has the ability to change the HAML download from http://mediacast.sun.com/users/tnorbye/media/org-netbeans-modules-haml.nbm/details to be a .nbm extension instead of a jar, I think that would be a 
great thing. I would not use an IDE that doesn't have decent HAML support. I gave RubyMine the 20 minute demo yesterday but ditched it bc it didn't highlight 
HAML and I couldn't be bothered. It would be a bummer if Ruby-ists ditched NetBeans for the same reason, since it DOES work once you figure out that you 
need to rename the .jar file into a .nbm.

thx

It works fine for me - clicking the download button leads me in NBM file download
http://mediacast.sun.com/users/tnorbye/media/org-netbeans-modules-haml.nbm

odd. i get org-netbeans-modules-haml.nbm.jar Safari 4 OS X. perhaps it's some odd mimetype thing. I presume you're displaying file extensions.