Very recently I worked on the issue where Task Updates were failing for one of the project plans in Project Server 2010. We initially thought it’s related to the performance, however that turned out to be false.

We found the below error in ULS log

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PWA:https://www.contoso.com/ProjectWebApp, ServiceApp:Project Server Service Application, User:P1PM, PSI: System.ArgumentException: Invalid start and end times     at Microsoft.Office.Project.DataEdit.Contours.Int64ContourEx.SetValueBetween(RelTime timeStart, RelTime timeEnd, Double value, Boolean treatAsUnits)     at Microsoft.Office.Project.DataEdit.Assignments.AssnCntr.RescheduleRemainingWorkAfter(AssnNode assnNode, DateTime dtAfter)     at Microsoft.Office.Project.DataEdit.Assignments.AssnCntr.SetPeriodActualWork(AssnNode assnNode, TaskNode taskNode, DateTime dtStart, DateTime dtEnd, Double wrk, Boolean fRollup)     at Microsoft.Office.Project.DataEdit.Assignments.AssnCntr.SetPeriodAssnActualWork(Guid guid, DateTime dtStart, DateTime dtEnd, Double wrk, Boolean f…

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This error indicates that there is something wrong with assignment start and end times. We found that this task is Manually Scheduled Task and resource for this task was setup to start on non working day (Sunday). We changed it to working day (Monday) and that helped to resolve the issue.