Error Too many threads in Player Settngs

I got "Too many threads" error popup whenever I opened player settings with existing projects. I got same error for both 5.5.3 and 5.6.0.

But new projects didn't make error popup.

Temporarily, I removed this error by doing below steps. Also, after upgrading to version 5.6.0, android app was crashed as well. I also solved crashed error with same steps:

1) Create new project.

2) Copy all files and folders under the Asset folder.

3) Reset player setting.

4) Remove image on "Static Splash Image" and change it with Logo

I guess some options on player settings might not be applicable for new version including "Static Splash Image".

Do you have any other way to solve this error?

Thanks, Young