Hi Rob,nThanks for replying. I found that when I define 14 global variables, it works as intended. However, once I define the 15th variables, I get this error. I changed the variable name many times and still the same issue. I even, used it with same name and removed one of the other 14 variables and the UDF worked fine. Now I am running the simulation with 14 global variables and I defined the 15th as local variable. It is working but I need to compile every time to change this variable the 15th.nI am just wondering is this a limitation in FLUENT, or I am doing something wrong? (I am doing this using an academic version)n