emake was unable to open the schedule data file indicated by [path] in the message. More detail about the cause of the problem is given by the system error detail in the message. When this warning appears, emake will not use schedule optimization, but will continue to execute the build as if the feature had not been enabled.
Because this failure involves an external system in this context (the filesystem on the emake host), the list of possible causes is virtually limitless: insufficient permissions; a corrupted filesystem; hardware failure; and so on. Refer to the specific system error message to determine the cause of the failure.
The fix depends on the cause of the failure. Since this is merely a warning, and not a error, the user may elect to simply ignore the message: the only effect will be on the use of schedule optimization in the build. The user could also avoid the issue by specifying a different --emake-assetdir, which would cause emake to use a different schedule file entirely.