Cause 1: There cannot be a Remaining Duration that is less than or equal to the remaining lag on an activity. This error will appear when trying to change the duration to a number less than the remaining lag.
Cause 2: This could be due to the activities being out of sequence.
Cause 3: This can also be caused by resources having an actual or current Start later than the finish date you are trying to assign to the activity.
Ensure the Remaining Lag is less than the Remaining Duration.
1. Go to the relationship tab and add a column for lag.
2. Verify that you do not have lag assigned to your resource assignment which is pushing out the remaining finish date for your resource. Check this by going to the activities view/resource tab and add a column for remaining lag.
3. If the lag is greater than the remaining duration of the activity then you need to reduce the lag before you change the remaining finish date on the activity.
Force the activity to finish on a certain date that is before the Remaining Early Start Date. Select to use progressed activities to schedule as Progress Override.
To change to Progress Override please do the following:
1. Tools. Schedule. Advanced tab
2. Select the Progress Override button
5. Change the date to required date.
Add a column in the resource tab for Actual Start and Start and verify that it is before the finish date. This only affects the date when the resource is driving