Why I got error reshape when I was using pdegrad?

I got error when I tried to calculate pdegrad using:

[ux,uy] = pdegrad(p,t,u);

The error is "Error using reshape".

I read some threads about this and they said that I have to have number of elements that are able to be divided each other between (p,t,u). Do my elements number of p, t and u have to be the numbers that if they are divided by each other will not give a fraction?

Thank you, Bella