the compiler cannot find the function. For us it is easy to know that the function is in the DLL tcmcsdll0050 but we must also tell this to the compiler!!
You could add tcmcsdll0050 to the list of Libraries. Just mark your DAL and call "libraries" option
... or you can add the library to the script as follows:
table ttccus020 | Project Order
table ttcmcs050 | First Free Numbers
table ttcmcs051 | Number Groups
#pragma used dll otcmcsdll0050 |Check order series
... and don't forget the "o"