Hi...this may be a question for Tech Support, as they can investigate in more detail. _URL may not be available to your stored process, depending on how you're submitting it. According to the explanation at this page
http://support.sas.com/rnd/itech/doc9/dev_guide/stprocess/reserved.html
...not all reserved macro variables are available from every client or on every server.
Also, attempting to write your own HTML in a DATA step program may turn out to be a separate problem. This web page:
http://support.sas.com/rnd/itech/doc9/dev_guide/stprocess/inet2stp.html
includes the statement that
If you are writing to _WEBOUT using PUT statements while ODS has _WEBOUT open, when you execute the code the PUT statement data might be out of sequence with the data generated by ODS. This problem occurs because both your code and ODS are opening the same fileref at the same time. For example, the following code might not always work as expected:
Refer to the above web site for more details and a workaround. Or, contact Tech Support for help with your specific problem.
cynthia