You need to read the documentation.
As stated in the documentation, if your code is not solid or needs to change often then use ExecScript as follows which will never lock anything:
"lcRetVal = EXECSCRIPT(FILETOSTR(oProp.AppStartPath+'\prg\myexternalfunc.prg'))
Alternatively, put your code in a seperate HTML file enclosed in <% %> and use the 'include' functionality. For example, <%= include('myVFPcode.htm') %>
Code used in this way is not locked by IIS so it can be changed at will without recycling IIS.
VFP code that is solid and won't change often can use the traditional ways: SET PROC TO, CREATEOBJECT, etc (see examples). This code will be cached by IIS."