Custom Workflow generates a thousand of Workflow Instances and EREs

Hi everyone,

I developed a Custom Workflow that complete user attributes information when a user select a value from a drop down list. I tested this workflow with a Request MPR  with an Action Type "Create" and the workflow Works perfectly. But now, I have to use this workflow in an Action Type "Modify" , when I changed it, the workflow Works fine but generates  a thousand of Workflow Instances and in consequence a thousand of EREs.

Can you help me please?

Thanks in advance,