Google Apps Script - You do not have permission to access the requested document

var sourceSpreadsheetID = "xxx";
var sourceWorksheetName = "xxx";
var targetSpreadsheetID = "yyy";
var targetWorksheetName = "yyy";

function importData() {
  var thisSpreadsheet = SpreadsheetApp.openById(sourceSpreadsheetID);
  var thisWorksheet = thisSpreadsheet.getSheetByName(sourceWorksheetName);
  var thisData = thisWorksheet.getDataRange();
  var thisData = thisSpreadsheet.getRangeByName("zzz");

  var toSpreadsheet = SpreadsheetApp.openById(targetSpreadsheetID);
  var toWorksheet = toSpreadsheet.getSheetByName(targetWorksheetName);
  var toRange = toWorksheet.getRange(1, 1, thisData.getNumRows(), thisData.getNumColumns())
  toRange.setValues(thisData.getValues()); 
}

I ran the above code and it worked perfectly for two days (it ran every 6 hours through a trigger) but suddenly, it stopped working and I keep on getting an error "You do not have permission to access the requested document". The source sheet and target sheet are in a shared drive, hence, there is mutual access for both sheets.

I am running the same script for a different pair of sheets, in the same team drive, and it is working perfectly.

I tried the following suggestions but to no avail:

• Google Apps Script error: “You do not have permission to access the requested document”