Not sure how to fix it,  but just experienced same thing. 

Got it fixed but not sure which corrected it. Recently upgraded from MAS90 v4.50 and SageCRM v7.1. Afterwards I started to receive that error message. Corrected two issues.

1. On the server the Integration Engine was stopped and disabled. I had to re-enter the password on the account being used, enable and then restart the service.

2. In MAS in the CRM Server Options panel there is now "Incidents" (wish there was some documentation on how that works). For Integration Server Port ID the value was now zero (0) instead of 8888 which it was in v4.50.  If I attempted to change it returned an error message : "The Sage CRM SQL server and database name already exists for another Sage CRM instance ID. You must enter a different Sage CRM SQL server and database name". However that was the only instance.  I then went into DFDM and found the CU_Company file and changed the value from 0 to 8888.  Things now worked. However if I go into the CRM Server Options panel, while it displays 8888 it returns the same error message if I hit Accept. I have to hit Cancel to get out.

I'm not seeing completely same things as you.  ie I don't have "Incidents" on the CRM server options panel.

Upgraded from 4.5 to 5.0 a few weeks ago.  Just set up a new demo CRM company and linked to ABC.

Everything seems to be syncing, ie integration engine is working fine.  It's on port 8888.  I don't have any of the same errors you're getting, except when I go to an opportunity and click on Quotes or Orders I get same "Illegal Access Attempt" error.

I checked CU_CRMServerOptions.M4T (I think you meant that table, not CU_Company) and things look good in DFDM too.

And I tried on 5.0, and just barely applied PU 1, and still no difference.

What version of SageCRM are you on? You should be on 2013.

If by 2013 you mean 7.1 SP2, then yes.  We're on the latest version of Sage 100 and the accompanying Sage 100 ERP 2013 CRM install.

Are you on Sage 100 Standard (MAS90) or Sage 100 Advanced (MAS200)?

Standard.

In the MAS_System folder look for CU_CRMServerOptions  and see what value is in Instance Port ID.

Make sure you do not have a backup of your XXX company in another company that included the CRM module.  So if you are copying companies - do not include the CRM module in the copy.

Evidently Johnny's an educated man, all those 90Mind sorts seem to be. Now I really admire him as I did not know that.