Please seek consultation from an attorney in your area on this matter and bring with you the settlement that you agreed to in the comp case.  Please tell me that you had a workers comp attorney helping you with the mattter.  The agreement with your employer  - without reading it  - should only be to allow them to be reimbursed for the payments made to you for medical care and lost wages.  It does NOT allow your employer to sue them on your behalf for the personal injury damages to you.  You have every right to do that.  Generally, you can not subrogate that type of claim.  Please seek help.  Good luck.