I was wondering if anybody has encountered this problem...some of my websheet are working and i can open and work on them but there are some that encounter an error and a dialog box pops up and says "55 Object Not Found".
Try reloading the navigation tree and open the web sheet again.
It is possibly the case that you have deleted and then re-Uploaded a web sheet using an existing name. (Which seems to be a requirement these days as Updating websheets gives me a pile of garbage when I reopen them.) The issue is that the code behind the navigation tree is still looking at a link to the old file, which no longer exists. Reloading the tree refreshes the XML so that it now looks at the new file.