"SYSTEM_FAILURE" error message when running BEX query

Hello,

I often encounter this error when I run BEX queries (take note that I encounter this error after I have already entered the query values). But when I run the same query in a later time, the query becomes successful, which makes the problem intermittent. I only encounter this when running BEX but I don't encounter such error when I'm running the query in RSRT and displaying it in SAP instead of in Excel. I hope you have any idea about this. Thank you.