Hi,
Is there any kind of error messages to work with here? I recommend you enable a few debugging and logging options so that you can catch what exactly went wrong.
1. SmartForms runtime logging (https://help.k2.com/onlinehelp/k2smartforms/userguide/current/default.htm#manually_debugging_forms.html)
2. Change logging settings in the SmartForms web.config file to enable logging output and specify logging target.
<add key="Forms.Global.ErrorLogging.Enabled" value="true" />
<add key="Forms.Global.ErrorLogging.FilePath" value="C:DebugSmartForms.Web.error" />
3. Server-side runtime errors in SmartForms will be logged in the following logfile:
Program Files (x86)]K2 blackpearlHost ServerBinSourceCode.Forms.Runtime.Error
4. Check your browser's developer tool. If there's any script related errors, it should show up in the console.