I would suspect someone, somehow while possibly navigating the MAS90\AP folder accidentally deleted/moved a file from there. I've seen cases where users accidentally dragged an entire module folder into another directory, this results in more than just one of the affected module's tasks complaining when attempting to launch them though.

Do you have 3rd party solutions?

Any recent changes to the sage 100 installation on the server? 

This is a new Installation. The AP folder is complete.  Yes there are enhancements and they don't touch AP.

Does the error occur before the task is displayed?

Yes it is. 

Can you include a screenshot of the error message?

Also, if it has an "Info" button, click that and screenshot the info window as well.

If you get that far, there should be a "printer" icon in the bottom right, click that and either attached the created .txt file or paste its contents in your reply.

No info button.

Also, include a screenshot of your Installed Modules Listing report.

Couple more things since you are on advanced.

Where is the error occurring, on the server or the workstation?

If workstation, all or just one workstation?

Have you tried uninstalling the sage 100 workstation, restarting the workstation, and installing the workstation by accessing MAS90\wksetup\autorun.exe through a UNC path and running it as admin?

Did you verify that the Modify or Full Control permissions have been set for the windows user on the MAS90's parent folder on both the server and the workstation?

EDIT: Make sure when setting the permissions on the MAS90's parent folder, that you check the option to replace ll child object permissions. You should make sure all pvxwin32.exe processes have been shutdown properly on the sage 100 server though since some will lock certain files.

Considering what's in your installed modules listing, i'm assuming this is a recent upgrade attempt and migration. Did you check the Link Maintenance Utility and check these two types for any scripts and make sure the records are pointing to the correct path?

If any scripts show up in that list, check if any scripts are occurring on the Post Load UI events. Check the MAS90\CM\Script folder on the server and look fr any script files that end with .M4L.vbs. You find some and one of them is named SY_Print.M4L.vbs, you can try renaming it.

How are you launching the task? Launching Manual Check and Payment Register directly from the menu or by clicking the "Print" button in AP Manual Check and Payment Entry?