Ios – Property not found on object of type

I have a simple question:

I have a NSManagedObject subclass that I've been using for some time and it was working perfectly fine.
Today I added a new property to it with the corresponding iVar. The property is a simple (nonatomic,retain) NSString *.
And as normal i added @synthesize to the property to generate setter and getter functions.
However, there is no way i can use the newly defined property!!! I keep getting "property not found on object of type" error and my build fails.

Here are a few chunks of code that will clear things out:

    //import the core data header first CoreData/CoreData.h

    @interface Contact :  NSManagedObject

    {
       NSString *contactID;
       NSString *firstName;
       NSString *myDevMod;
    }

    @property (nonatomic,retain) NSString *contactID;
    @property (nonatomic,retain) NSString *firstName;
    @property (nonatomic,retain) NSString *myDevMod;

    @end

and the corresponding .m implementation:

    #import "Contact.h"

    @implementation Contact 

    @synthesize contactID, firstName, myDevMod;

and the code that uses the Contact class:

    #import "Contact.h" //at the start

    Contact *aContact = [[Contact alloc] init];
    aContact.contactID = someId; //works perfectly fine
    aContact.firstName = someName; //works perfectly fine
    aContact.myDevMod = @""; //THIS IS WHERE THE ERROR OCCURS!!
    [aContact doSomethingHere];
    [aContact release];

What do you think could be the error??

Thanks in advance for your support.