Don't know how to fix simple ERROR!

I am trying to replicate Gertler, Sala, and Trigari 2008. When I run the code for the simulation I get:

“ERROR: my_GST.mod: line 252, cols 10-15: syntax error, unexpected NAME”

Lines 251 and 252 are:

shocks;
variance Sigz_t = sigmaz^2;

Sigz_t has been declared as an exogenous variable at the start.

I don’t know why this problem is happening, any help would be very appreciated.

I have attached my .mod file.

my_GST.mod (6.8 KB)

Best,

You forgot to close your model block with
end;