That function was added in VENUS 4 so if you have recently imported methods written in VENUS 3 into your VENUS 4 and selected Overwrite all, it probably overwrote the HSLPTL libraries with an older version.
Here are the default HSLPTL library files from VENUS 4. You can try overwriting those in your HAMILTON\Library folder.
Also, as Starrif2263 mentions, double-check that you don´t have any HSLPTL library files imported in your HAMILTON\Methods folder. If in the method there no specific path defined for a library file, VENUS looks for that file in this order:
1) In the current directory.
2) In the directory that is listed under the registry key Methods.
3) In the directory that is listed under the registry key Library.
4) In the directories that are listed in the PATH environment variable.
I hope this helps!