Ohh Jesus!!! What does this means... "Invalid text value. A text field contains invalid data. Please check the value and try again."

You may get the following exception when calling the Update method of the SPListItem class:

Microsoft.SharePoint.SPException was caught
Message="Invalid text value\n\nA text field contains invalid data. Please check the value and try again."
Source="Microsoft.SharePoint"
ErrorCode=-2130575336
StackTrace:
at Microsoft.SharePoint.Library.SPRequest.AddOrUpdateItem(String bstrUrl, String bstrListName, Boolean bAdd, Boolean bSystemUpdate, Boolean bPreserveItemVersion, Boolean bUpdateNoVersion, Int32& plID, String& pbstrGuid, Guid pbstrNewDocId, Boolean bHasNewDocId, String bstrVersion, Object& pvarAttachmentNames, Object& pvarAttachmentContents, Object& pvarProperties, Boolean bCheckOut, Boolean bCheckin, Boolean bMigration, Boolean bPublish)
at Microsoft.SharePoint.SPListItem.AddOrUpdateItem(Boolean bAdd, Boolean bSystem, Boolean bPreserveItemVersion, Boolean bNoVersion, Boolean bMigration, Boolean bPublish, Boolean bCheckOut, Boolean bCheckin, Guid newGuidOnAdd, Int32& ulID, Object& objAttachmentNames, Object& objAttachmentContents, Boolean suppressAfterEvents)
at Microsoft.SharePoint.SPListItem.UpdateInternal(Boolean bSystem, Boolean bPreserveItemVersion, Guid newGuidOnAdd, Boolean bMigration, Boolean bPublish, Boolean bNoVersion, Boolean bCheckOut, Boolean bCheckin, Boolean suppressAfterEvents)
at Microsoft.SharePoint.SPListItem.Update()

This occurs when the value you supplied for a text field is larger than 255 characters. To address the problem, store less text in the field or change the field type from text to note.