50G cant graph x^2

[BINUBALL]

if i want to graph something, i press LS+F1 but i get a error "No Current Equation". so i purge EQ and i can into plot screen. and press LS+F4 and type x^2 in EQ, then press ERASE DRAW i can graph a func.
but if i exit plot screen and go to LS+F1, ERASE DRAW doesn't graph a func. so i press ON+F3 for warmstart. then i get a variable EQ with value PTR D4B55.
if variable EQ with value PTR D4B55 stay in directory i cant get into plot screen. (LS+F1) get a error "No Current Equation"
i can graph Y30(x)=x^2 (in LS+F1 memu) i say i cant graph x^2 (without Y30(x))

can you explain this strange behavior of 50g? and do you know what is the PTR D4B55?
++
in my graphing directory, there are four 'x' variable with value -6.5. can 50g have mutiple variable with same name?