Microsoft is working on my case to solve the issue I have with attachments in InfoPath. Today I found this error registered in Event Viewer on the MOSS server:
Event Type: ErrorEvent Source: Office SharePoint ServerEvent
Category: Forms Services Runtime
Event ID: 5760
Description:InfoPath Forms Services has detected a mismatch between the user’s data in the browser and on the server. This may indicate the SESSION_STATE_PASCAL_CASED is not configured properly on a multiple front end farm or that a malicious user is trying to tamper with client data. (User: domainxx, Form Name: Testform, IP: , Request: https://xxx/_layouts/FormServer.aspx?XsnLocation=https://xxx/Testform/Forms/template.xsn&SaveLocation=https://xxx.se/Testform&Source=https://xxx.se/Testform/Forms/AllItems.aspx&DefaultItemOpen=1, Form ID: urn:schemas-microsoft-com:office:infopath:Testform:-myXSD-2008-04-29T14-39-23)
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.