Nextion 7 inch DIsplay - file gets to large

Using Arduino Displays
7 
       Serial2.print("ErrorMsg_");
         Serial2.print(z);                 // z is the variable from your example
         Serial2.print(".txt=\"");
         Serial2.print(variable);
         Serial2.print("\"");
         Serial2.print("\xFF\xFF\xFF");

From my Tutorial you can see adout "

at : How to change components' attributes at Nextion from Arduino:

and also How to make a useful pop-up message on Nextion