Actually nothing changed about it, I believe the null reference happens only under .NET 4, it worked previously under .NET 3.5. The only change may be that I made it not use the special handling by default unless you add the config setting I mentioned. I did this to avoid the error under .NET 4.
Maybe you can look in mojoPortal.Web.Framework.CutlureHelper. GetPersianCulture() and figure out a solution for .NET 4. The current code was not implemented by me but by Asad Samarian. I'm not sure what has changed in .NET 4 that may affect it.
Persian Calendar has not been well supported in the .NET framework so very hacky solutions have been used. I'mnot sure if any improvements are available in .NET 4, maybe you could look into it.
If datepicker does not support specific culture then it should work based on Georgian!
I'm not sure everyone would agree about that. A lot of work was done by Asad to make dates display for Persian in the blog a while back but I have left such efforts up to Asad and anyone else who uses Persian culture to find solutions. Asad had me comment out some code not too long ago due to feedback from another Persian language user in the community. So this also could account for diference with the Persian community site which has not been upgraded in a while.
We have a provider model for DatePicker so other date pickers could be plugged in. I think there is a .NET Persian DatePicker on the web (at least there was one last time I looked into it) that is free but is not open source and cannot be included in mojoPortal but it may be possible to implement a provider for it and plug it in to mojoPortal.
Best,
Joe