I cannot proceed with publishing the workflow whenever I add more steps. But if I create a new workflow and copy the steps there, it works. Does the 2010 workflow have limited number of If statements that it allows?
Each workflow is associated with a XOML file, please check for the difference of XOML settings in New and associated workflow, you can check XOML file with the help of SharePoint Designer. You will certainly get some idea. As per my knowledge there is no such limitation, there might be some custom Workflow activity which is not available after association.