Symptoms

When user tries to open task from worklist or task link from notification mail he receives an error:

The constructor to deserialize an object of type 'SourceCode.Forms.Runtime.ThemeNotFoundException' was not found.

This error happens from time to time (once a week or so) and can be "fixed" by restart of k2 smartform application pool.
 

Diagnoses

Based on previous cases where similar error was reported it is possible to say the following:

1) Based on error message text (ThemeNotFoundException) it is possible to assume that one or more forms which you are using uses custom theme which is absent in your environment. Package and Deployment does not include custom themes into packages and if you have custom theme in your development environment which is missing in environment where you receiving this error you have to check this and if necessary to add missing theme manually.

2) This issue can also be caused by the fact that not all forms were checked-in and it maybe resolved by performing check-in operation for all forms issue was resolved. Note: for clients any form changes become visible only after check-in operation and not immediately after Save. In that respect check-in for forms is way of deploying changed forms.
 

Resolution

Make sure that all required themes are present in your environment and try to check in all forms.