Unable to Raise Forest Functional Level from Server 2008 R2 to Server 2016

You cannot raise the Forest functional level above the lowest OS version running on a domain controller... As long as you have 2008 R2 boxes you are stuck at that level...

Thanks Scott. Sorry forgot to mention. I have 2 2008 DC's and 2 2016 DC's in the forest. I moved all FSMO roles from the 2008 boxes to the 2016 boxes. all I have left is the raise the forest function level.

Did you remove the 2008 boxes? They have to be completely removed from AD roles and if they don't come out completely you will have to clean up the leftovers.
Functionality is limited to the OS of ANY boxes in the system as domain controllers.  So as long as you have 2008 DC's in the forest at all you can't raise it.

Nope, the 2008 boxes are still there. So we have 2 domains with a trust in the middle. The other domain I did the exact same thing and I was able click the option to raise it. same exact setup as the first domain. I have pics attached to show.
Forest1.PNG
Forest2.PNG

Scott Silva has 100% given you the correct answer. The LOWEST version DC in an environment is the HIGHEST you can raise the functional level in that environment.  It creates a boundary you can't get past.

You have forest and DC functional lvl.
Forest functional must be the lowest version on you entire network of Windows server
and the same goes for DC functional lvl, just that this one is related to domain controllers instead of any server.

Show the points to Scott :P haha

can you all explain why I have that option on my other forest? Also, I was able to raise my forest and domain function from 2000 to 2003 with no problem previously.

Are you saying you were able to raise your forest and domain functional levels from 2000 to 2003 while there were still 2000 domain controllers?!?  I doubt it.

The options available are dictated by the version of DOMAIN CONTROLLERS in your environment (NOT JUST MEMBER SERVERS.)

If you were able to raise a domain functional level to 2016, I can almost gaurantee you, as in I'd bet my firstborn child, that domain only has 2016 DCs.  It may have older member servers. But all the DCs are 2016 or higher. Short of remoting in to prove it to you though, I'm not sure what else to say.

I think you are all correct. After doing more research and remembering what I did to move us from 2003 to 2008, I did realize that you do need to be at a higher level before moving the function up.
Thank you all for your help.