Hi,
When you make correlations, I would advice you the correlation step and the next step on which the server will send the dynamical value, which needs to be correlated, to be outside web_concurrent_start(NULL); web_concurrent_end(NULL); block.
web_reg_save_param_xpath registers a request to find an XML node within the server response to the next action function. However when you have a concurrent group all the functions within the concurrent group are executed together.
Kind regards,
Vesela