When I deployed my custom WebPart to page on WebSite I got the message in the webpart body:“Web Part Error: Sandboxed code execution request failed."

I  created a simple SharePoint project as a Sandboxed solution , added an WebPart to it and
deployed the wsp file to the Office 365 team-site.  Next I added a test page and then added my custom WebPart to that test page. It all  was OK!

But when I deployed my custom WebPart to page on WebSite  I got the message in the webpart body:“Web Part Error: Sandboxed code execution request failed."

I would be grateful if you could give me information why I  get  this error message.

Thank you in advance!

Yours faithfully,

Slavi EPopov