Error:requiring an unknown u for the problem

I have definite the problem and solve, the software said,
I don’t know what is wrong.

Look at Dirichlet condition
On(… , u= …)
I think you use an other variable
On(…, ???)

you mean the solve (u1) and on (u1)? they match,right?

Can you send me the instruction of the line 248

After changing the boundary condition,it works. Thanks for your advice.