Variables used in query desinger for portal

hello all,

I am developing few reports and whenever I use a varaible with SAP exit it errors out on Portal with errors like

"Initial RANGE-LOW for customer exit variable 0P_FVAEX corrected to #

No value could be determined for variable 0P_FVAEX."

"Variable 0I_PCURR could not be replaced."

What might be the issue here ?

Thanks,