ok... first off, you can't change the value of constants that you declare. The problem is that every time you run the program, windows loads the file into a different location so you can't declare filein as constant. The same goes with read1$ because theoretically, the contents of the file could change each time the program is run. So, you need to change all of the const commands in the program to global (for a variable), or just leave it out all together.
Your next problem is that you don't understand just how the data command works and I suspect that you probably don't need it for your level creator at all. You see, the data command can only be used to store large amounts of information that don't change whenever the program is run. So data command lines are similar to const lines that store a lot of information. In addition, you have to use more commands to access the information that you stored with the data commands. Specifically, you should look into the restore and read commands if your still interested in using the data command.
However, I don't believe you need to use this command because you said that you were building a save command into your program. You usually save information into files and don't use the data command at all. normally you would use the writeline, writebyte, write-whatever, commands to save information.
Your next problem is that you don't understand just how the data command works and I suspect that you probably don't need it for your level creator at all. You see, the data command can only be used to store large amounts of information that don't change whenever the program is run. So data command lines are similar to const lines that store a lot of information. In addition, you have to use more commands to access the information that you stored with the data commands. Specifically, you should look into the restore and read commands if your still interested in using the data command.
However, I don't believe you need to use this command because you said that you were building a save command into your program. You usually save information into files and don't use the data command at all. normally you would use the writeline, writebyte, write-whatever, commands to save information.