Usually, the first problem is development environment change and new development tools. When you move from one programming language to another or change technologies, third party libraries or something else there is always a risk of potential problems with it. That is why you shouldn’t start using new technology/language before you have at least few experts in it. In general the idea to learn new technology/language by developing a real important project is bad. Pilot project should go first and in pilot project you may resolve all potential technical problems. It is better to blog about pilot project progress and problems, in this case you can always obtain list of problems/solution.
The second problem (and the most significant) is that development from scratch leads to repeating bugs and issues that were already fixed in previous product. The simplest way to solve this problem is try to repeat all issues from previous version of product in current version It’s possible if you used Bug Tracking practice, but if not, you are in troubles. And in any way it will be hard, because there can be thousands of issues. Also it doesn’t insure against new issues in a new product.
Another way is usage of Test Cases from previous project. If project was developed accurately then every idea, every business rule, every potential issue was reflected in proper Test Case. Usage of Test Cases from previous product version helps control quality from the start.
The third problem is should you use or not some parts of code from previous project. On the one hand you save time by reuse already developed and tested code, on the other hand you developing from scratch to stay away from the mess of old code. In most cases you should refactor before reuse that will solve the problem.
In general development from scratch is not recommended, but to be frankly, usually we do not start new version of product completely from scratch. We have documentation, user’s requests, issues database, project backlog, test cases and many other useful stuff from previous project which can be and should be used.