A bug notification in DHIS2

Dear Sir or Madam,

During the process to make the third data entry form for a program(all camcer2) in DHIS2 (version number 2.28), I recieved this bug notification "an exception occured sorry! The system failed to execute the operation. Usually, no dara is lost and you can continue working by going back to the previous page" , but I cannot continue preparing the entry form by going back to the previous page. I started to prepare a new program with those data entry forms but I recieved the notification again. Could you please help me to solve this problem. I'm looking forward to hearing from you as soon as it possible.