Need solution to Invalid widget Html ,error 5000?


Hi I am newbie to blogging.and i started customizing the blog by placing the recent posts widget and all.It has been GOING well till now but today i have been facing a severe problem regarding the widgets. When i tried to place the recent post html code into my blog from mbt it is getting saved but when i opened the blog it is not getting displayed,and when i tried to remove it it showed Invalid widget Html ,error 5000.and it got removed automatically and also i have disabled the navbar it got enabled.I have checked my webmaster for security issue but it showed me no issue. I would like to know whether my account got hacked or any fault with the html code . Hoping for the solution at the earliest.