This bug was originally marked as duplicate of bug 247884, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE 8.1 Beta (Build 201507231027)
VM: Java HotSpot(TM) 64-Bit Server VM, 25.60-b23, Java(TM) SE Runtime Environment, 1.8.0_60-ea-b25
OS: Linux

User Comments:
GUEST: first after installation. import previous setting.

GUEST: importing plugins from 8.02

gholmer: Accepted dialog box to import plugins from previous installation on first run.

mdeggersbeans: This happened when I was importing Netbeans 8.0.2 plugins into the nightly build. Some of the plugins have not been updated yet, so this may be causing the issue.

roti: In 201503250001, Imported all installed modules from 8.0.

dathyrius: Importing plugins.

cezariusz: Importing plugin

marckoby: upgrade to dev

roti: installing plugins from previous version




Stacktrace: 
java.lang.IllegalStateException: Module org.netbeans.api.progress/1 is already enabled
   at org.netbeans.ModuleManager.attachModuleFragment(ModuleManager.java:1019)
   at org.netbeans.ModuleManager.maybeAddToEnableList(ModuleManager.java:1585)
   at org.netbeans.ModuleManager.maybeAddToEnableList(ModuleManager.java:1595)
   at org.netbeans.ModuleManager.maybeAddToEnableList(ModuleManager.java:1595)
   at org.netbeans.ModuleManager.simulateEnable(ModuleManager.java:1534)
   at org.netbeans.ModuleManager.simulateEnable(ModuleManager.java:1508)