Test code succeeds in sandbox, and fails in production test after deployment

•     Setup-àDevelop --> Apex Text Execution
•     Checked Disabled Parallel Apex Testing

•   Clicked the link "View Test History" ( Clear Test Results.)

• SetupàDevelop --> Apex Classes-àClicked "Compile all classes"
•  Click On "Estimate your organization's code coverage" 
• Clicked Run All Tests 
•  Run  Apex tests again.