mkdir() says theres no such directory and fails?

Question

Im likely doing something very simply wrong, but when I try to make a directory (using a variable of an insert just performed as the last folder name), I get the error:

Answer 1

in my case $insertID was generated from some data as string by concatinating

$insertID=$year.$otherId;

I simple rewrote code like this and error disappeared:

$insertID=(int)($year.$otherId);