Hi all,

One of our clients is experiencing an intermittent error when attempt to save a node in the back office. The event log shows the following:

Event code: 4009 
Event message: Viewstate verification failed. Reason: The viewstate supplied failed integrity check. 
Event time: 24/02/2015 12:24:01 
Event time (UTC): 24/02/2015 12:24:01 
Event ID: d9cee2b8e9644341a07b21d82c8d1103 
Event sequence: 49723 
Event occurrence: 2 
Event detail code: 50203 
 
Application information: 
    Application domain: /LM/W3SVC/1/ROOT-5-130691580454402645 
    Trust level: Full 
    Application Virtual Path: / 
    Application Path: F:\inetpub\xxx\ 
    Machine name: xxx
 
Process information: 
    Process ID: 3724 
    Process name: w3wp.exe 
    Account name: IIS APPPOOL\xxx
 
Request information: 
    Request URL: https://xxx:443/umbraco/editContent.aspx?id=42052&isNew=true 
    Request path: /umbraco/editContent.aspx 
    User host address: xxx.xxx.xxx.xxx
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: IIS APPPOOL\xxx
 
ViewStateException information: 
    Exception message: Invalid viewstate. 
    Client IP: xxx.xxx.xxx.xxx
    Port: 54048 
    User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36 
    PersistedState: xxx
    Referer: https://xxx/umbraco/editContent.aspx?id=42052&isNew=true 
    Path: /umbraco/editContent.aspx 

Has anyone seen this before? It's an Umbraco 6.2.4 site.