414 Request-URI Too Large / Bug

Hi! I created a free account on erpnext.com to test the ERP. Soon I tried to change default series in Sales Order and a tab in Chrome stopped responding. Refreshing, restarting computer does not help. I am getting the same message in browser window. Could you tell me how it can be fixed? Or where to ask for help?
The message is:

414 Request-URI Too Large

Fixed by clearing cache