You can try re-running the part of the original DB create script that adds those product types in. Make sure you have a backup of the DB before you do that of course!
Code:
set IDENTITY_INSERT [dbo].ProductType ON;
INSERT [dbo].ProductType(ProductTypeID,Name) values(1,'Generic Product');
INSERT [dbo].ProductType(ProductTypeID,Name) values(2,'Kit Product');
INSERT [dbo].ProductType(ProductTypeID,Name) values(100,'Gift Card Physical');
INSERT [dbo].ProductType(ProductTypeID,Name) values(101,'Gift Card Email');
INSERT [dbo].ProductType(ProductTypeID,Name) values(102,'Gift Card Certificate');
set IDENTITY_INSERT [dbo].ProductType OFF;