The value returned from LookupTask is a Long data type so don't use the ToInt32 conversion.

All numeric object handle references using the "n" prefix returned by sage 100 objects will be the Long data type unless you use the "o" prefix" in which it will return the object handle as an object.

I converted the datatype to long and I still got the same error- Lookup program failed. The task id \"000000000\"  is not on file.

Code- 

long taskID = (long)Convert.ToInt32(oSS.InvokeMethod("nLookupTask", ui)); 

why do you still have Convert.ToInt32 on that line?

The ui class you are using is correct, so it should be returning a value greater than zero. if it isn't, it is possible that the system is not configured for that task, so if you were to try to access that task through the desktop, you would probably get the message saying "setup indicates that this option is not available on your system".

It gave me "Specified cast is invalid error" when I tried to convert the object to long directly. I think the return type object only accepts Int.

If the task is not accessible from desktop, does that mean I cannot pull the data using ui? It probably doesn't give a taskID in such scenario. Is there any other way to pull that data?

Have you verified there is data in that object's table?

If there isn't anything in it, than it is possible the option was never turned on and that could be why you aren't getting a task ID returned.

This is the table.

https://help-sage100.na.sage.com/2019/FLOR/index.htm#File_Layouts/Accounts_Receivable/AR_CustomerShipToTaxExemptions.htm

If you have to, you can always read the data through ODBC.

Perhaps you should try getting a simpler object handle to make sure things are working properly, try CI_ItemCode_Svc. Try using "IM_Item_UI" as the UI task to lookup.

Yes, I have verified the object table and there is data in it. I already have similar lines of code for AR_Customer_ui, IM_Item_ui and some more and they all work, no issues. I'm seeing this issue only for CustomerShipToTaxExemptions.

Can you check the string property of oSS called LastErrorMsg (you'll need to add the "s" prefix, i.e. sLastErrorMsg) after the LookupTask method to see if it has anything helpful in it?

I added this line Convert.ToString(oSS.InvokeMethod("sLastErrorMsg")) right after LookupTask method. It's returned empty string.

It isn't a method, it is a property.

This line oSS.GetProperty("sLastErrorMsg") returned empty string as well.