My experience with some platforms would lead me to believe one of 2 things is occurring here.
1. The PLC is currently being accessed by another computer/person who is online with the PLC and performing edits. Or...
2. The project you have aquired is a snapshot of a program that was taken while someone was online with the processor and the Lock file that is generated by the software is set. Concept may generate a lock file when online with a processor for internal purposes.