This issue happens with me as well. I have developed Dashboards on BICS connections and using Flash variables as well.
Flash variables are to pass values from SAP EP to Dashboards as users view reports on EP.
I get this error for the no. of BICS connections i use in my dashboard. initially i thought its an issue with EP but it was not. still the issue is unresolved for me.
This usually happens when in a single session i refresh the report lots of times and also if i have a considerate time gap in between the refreshes. EP has a larger timeout hence i am able to refresh but seems my BICS interface is not able to hold that much parameters value or time period. i am still in contact with Admins to resolve the issue.
As a workaround i have to clear the browser cache and restart the IE and then it works again.