I'm trying to export all my old sonar projects as OMF however when I go to export them, OMF option is grayed out. Any solution?

How are you doing it?.  When I have done it, and I've been doing it recently. I select all the tracks I want to be in the OMF  and either have them embedded or if that doesn't work as separate files.  Its not hard.  

is your project only midi?
 
i think only audio can be export as OMF

It would be in your best interest to weight out weather or not you want to store Cakewalk projects as .OMF .
If you are just trying to transfer some projects using .OMF to use in another DAW than that is fine but I would'nt switch all of them over to .OMF.
 
When I read "All of my old Sonar projects" I had to stop and say, "don't do it" unless you plan on making back ups and keeping them. Especially with Bundle files. There are cases where they wont open.
 
Store .CWP with the Audio folder tucked nice and neat in a sub folder (project folder).
Then if you want, use WinRAR to wrap them up for a latter date.
 
Also be aware that:
The OMF file does NOT supply the following data and information:

• Volume and pan envelopes—OMF does actually support limited automation. However, as with Nuendo and most other OMF host programs, Gains and Pans are ignored (on both read and write) in SONAR as they are only supported on MONO tracks (OMF limitation).
• Plug-in effects.
• MIDI data.
• Tempo.

Myself I see no value in using OMF. Your better off saving your projects as a midi files and then having all your audio tracks sorted out so they play from end to end and exporting them as stems. 
 
I just tried this and managed to set up a Sonar project in Cubase. 
I saved the project as a midi 1 file. 
I opened that to Cubase which set the tempo etc.
I inserted all the same VST's I had used in Sonar, AD2, DIm Pro and Air stuff. 
Then I draged and dropped the audio from my Sonar folder onto some audio tracks in Cubase. 
Then I duplicated some of the effects, only big bummer is Pro Channel is of course missing, but Cubase has a few that are close and worked just fine. End results was the song played more or less the same. 
 
I'm not switching to Cubase anytime soon but it was good to see that if all else fails i can carry on with a few potholes. It's funny I bought Cubase Elements 7 a few years ago when I was mad about the way Sonar was going. It was only $100 so has been a good back up DAW. 
I also tried this with MIxbus but it keeps crashing. I see they just released an update, but I sort of gave up on it. It was only $30 and that's about all it's worth from the looks of it. 
If Cubase only had Pro Channel and a smart tool !