This is after trying Windows 10. I have reinstalled the latest Sonar, check for updates on everything. It was working earlier and now it isn't. Any ideas?

Did you reinstall the Presonus driver?

No..I'll try that. I did install the latest driver before upgrading to Win 10. Harrison mixbus 2.5 and 3.0 work fine.

Didn't help. Still get the same message.

When SONAR was reinstalled, was it a clean reinstall? IOW, was the registry cleaned prior to reinstalling. If not, try re-personalizing SONAR by holding the CTRL+SHIFT when starting SONAR. This will reset the ini files and some registry entries back to default values.

I may have found it. My sound card changed the buffer settings to 2048. I switched it back to 64 and Sonar is working. I wonder how that setting changed before I re-installed the driver?
I wonder if I should still try the clean install thing?

If the buffer change fixes the problem and it sounds like a good candidate. I would not mess with anything else.

Strange stuff. sometimes it works and sometimes it doesn't...I just keeps switching the settings around, back and forth until it works. I'm trying figure out a sequence which messes it up everytime.

It seems that after closing Mixbus...I have the problem with Sonar. Both are set the same. 64 buffers 48khz. When I get the message that Sonarplt.exe has stopped working and must close...I can swith the buffers to any other setting and then back to 64. close Sonar, and then Sonar will work the next time I open it.

Again...I open Mixbus 3.0 played it for a couple of seconds and saved project. Then close Mixbus.
I open Sonar and get the message. Open the soundcard and everything is set fine, but I have to switch it, and then switch it back for Sonar to work. Very Strange. Is Windows 10 worth it? Not to me. I'll try to find a solution, but Windows 7 is looking pretty good to me.
I believe this could be a compatibility issue between my 44VSL and Windows 10. I'm sure Sonar is fine. I haven't even considered this a Sonar problem. If I keep Windows 10...I'll probably need a new soundcard.