3D plot. Invalid expression. Why?

I am trying to plot a simple function but I get error:

Z = -25.6+ ((1/(1+10^(7.6-X.)))*(-24.6+Y.));

↑

Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched

delimiters.

Code:

x=(5:0.1:10);

y=(0:1:50);

[X,Y]=meshgrid (x,y);

Z = -25.6+ ((1/(1+10^(7.6-X.)))*(-24.6+Y.));

When I try other functions it works but not this one.

Answer 1

[Walter Roberson]

Z = -25.6+ ((1./(1+10.^(7.6-X))).*(-24.6+Y));

in particular no periods after X and Y

[Zaid Assaf]

Doesnt work either

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 3.279373e-132. 
> In mpower>generalMpower (line 107)

[Walter Roberson]

there is no / or \ operator in the code I posted.

You might not have noticed that I also changed the / to ./ and ^ to .^