Error Updating Id from a table

Hello everyone. I have a question because I'm trying to do a massive update of the Id from a table. This is the code.

SET @number=10000; UPDATE MyTable SET nId = @number+1;

It's a very simple code... I know. I'm just trying to update the Id starting with the number 10000 The problem is that I'm getting error because of duplicates on my primary key. It might be easy to fix it but I'm just starting with Heidi. I hope someone can inspire me... Hope everyone have a nice day! PD: Sorry for my bad english.