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Error: Validation of viewstate MAC failed

Error Message

Validatir. on of Viewstate MAC failed. Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. This error comes up in SchoolLogic Government Reporting.

Resolution

Download and run this script, which can take as long as 15 minutes. 

Check out these things in your IIS:

1.Launch IIS.
2. On the left side, expand items until you find SchoolLogic Goverment  Reporting.

3. Click SchoolLogic Government Reporting.

4.  With it highlighted, on the right side, click Basic Settings. Write down the name of the Application pool which Government Reporting is assigned to.

5. Back on the far left, go to the top and Click Application Pools. 

6. When the screen in the middle changes, double-click on the Application Pool from Step 4.  It should be using .Net 4.x. Change it, if it is using anything less. Close the pop-up window in which you make that change.

7. From the list of Application Pools in the middle screen, Highlight your Application Pool, then click Recycling on the far right. Remove regular time intervals and set a Specified time, sometime after regular usage times. 12:01 a.m. can be a nice choice.
8. Click Next. Click Finish.

SchoolLogic Web Config file

1. Go to the SchoolLogic Web,config file usually found here: C:\inetpub\wwwroot\SchoolLogic\web.config.
2. Open the Web.config file and click the cursor at the top line.
3. Enter CTRL – F.
4. When the search window opens, enter Pages

5. Click Find Next until you see a line like this:

   </pages>
    <compilation debug="true" targetFramework="4.0">

6. If yours is set to something else, change it to False, as shown here:

   </pages>
    <compilation debug="false" targetFramework="4.0">

Save the web.config file.