Code L is a deemed distribution because you left the company with an outstanding 401k loan balance. Since the loan can only be repaid via payroll deductions, if you leave with an outstanding balance, you have 60 days to payoff the loan by sending money to the 401k plan, otherwise the balance is considered a taxable distribution to you.
If this is the case, you may have other options. If you think you fully repaid the loan, you will have to prove it to the 401k custodian and get them to issue a corrected 1099-R.
This answer has been verified for accuracy by an Intuit expert employee
