As a network assistant for my school I was getting this error and a more experienced assistant fixed it but would not tell me how. Now, he has graduated and we have just made major changes to the share-point site and all my old forms are getting this error again. The code is c#. I tried re-uploading the forms from the server so they would be from the farm-administrator. I disabled and re-enabled the sandbox service. I tried the "allow code only allowed Infopath filler" checkbox both checked and unchecked. Still the same error. Please excuse that i don't have the full name of the error; i can post that tomorrow. I will have 45 minutes to work on this each morning till Friday due to the school being locked then it must be fixed. Any help is appreciated!