After upgrading DNN to 9.1.0.237, I am not able to add New module or add existing module.

I am getting following error:

main.js?cdv=104&t=0.49754237527650247:22 TypeError: Cannot read property 'data' of null
at Object.onClick (AddModule.js?cdv=104&t=0.24310857120769924:17)
at main.js?cdv=104&t=0.49754237527650247:182
at main.js?cdv=104&t=0.49754237527650247:103
at Object.init (AddModule.js?cdv=104&t=0.24310857120769924:10)
at main.js?cdv=104&t=0.49754237527650247:101
at Object.execCb (require.js?cdv=104&t=0.49754237527650247:1650)
at Module.check (require.js?cdv=104&t=0.49754237527650247:861)
at Module. (require.js?cdv=104&t=0.49754237527650247:1113)
at require.js?cdv=104&t=0.49754237527650247:132
at require.js?cdv=104&t=0.49754237527650247:1156

Thanks in Advance

Thanks,

Thanks Joseph for the quick reply.

Yes, I am using custom skin. Since I am new to DNN, can you please let me know how to switch the page to a standard skin?

I was facing the issue while upgrading to 8.0.3 and getting error while installing Google analytics component, it stuck during the installation and didn't complete However, it installed database changes successfully.

Thanks,
Kumar

I wanted to provide my update - I solved my issue:  I upgraded another  site to 9.1.0 and during the install noticed the installer never reached 100% but the site still came up as normal when you browsed to it.  I investigated and found some of the modules did not install/upgrade.   I simply browsed back to the install path and went through the motion of the upgrade again, I did this twice and finally - it works as expected, and now the upload install extensions work as expected.