According to page 16 of the owner's manual, you cannot disable child lock without the remote. Because you have lost the remote, the unit does not offer a manual way to disable that feature. I am not sure if a universal remote will allow you to enter the setup menu, and turn the child lock OFF. You could try that - it might work.
Or you could try contacting them:
Phone (480) 922-0896 or (800) 736-7679 (during business hours)
E-Mail [email protected]
Web www.govideo.com or www.sonicblue.com
They may or may not be able to offer further assistance. The universal remote might help, if you cannot get the original replacement for your unit.
Personally, child lock in DVD players is a pointless and unnecessary extra feature that should not exist; it should really only apply to Blu-Ray/DVD recorders.