[fpc-pascal] Illegal counter variable?

[James Richters]

Can someone please tell me why this happens?

Var
   I : Longint = 0;
Begin
For I := 1 to 6 Do
   Writeln(I);
End.

This gives me :
initialize.pas(4,5) Error: Illegal counter variable 
initialize.pas(6,4) Fatal: There were 1 errors compiling module, stopping 
initialize.pas(0) Fatal: Compilation aborted

but this works fine:
Var
   I : Longint;
Begin
I := 0;
For I := 1 to 6 Do
   Writeln(I);
End.

Shouldn't these two programs be identical?  What difference does it make if I initialize the variable in the Var section?

James