Cannot open project - says an error occured (ex param cannot be null)

One Star

Cannot open project - says an error occured (ex param cannot be null)

Help!  This is the 2nd time this has happened this week.  The first time I uninstalled and reinstalled Talend completely (currently on TOS 6.0.1)  But I can't keep doing that and losing productivity time waiting for everything to happen, then reloading all of my projects into the program.
What is causing this error to happen and how do I resolve it? 
One Star

Re: Cannot open project - says an error occured (ex param cannot be null)

Try going to the .Java folder within your Talend directory (mine is located here: C:\Program Files (x86)\Talend\TOS_BD-20150908_1633-V6.0.1\workspace). 
Within the .Java folder, delete the "src" folder. 
This should solve the problem -- it did for me. 
Employee

Re: Cannot open project - says an error occured (ex param cannot be null)

Not sure if that works.  Didn't work for my case.  I've been told to shut down TAC and kill all java processes.