When exporting a List view's data to excel using the Export to Excel feature, the Excel file is not created and you may receive an error similar to the following.
The Open XML SDK for Microsoft Office is required to be installed on all IIS servers hosting SmartForms runtime. This is used by K2 to generate the Excel file when you use the Export to Excel feature. If this dependency is removed from the IIS server at some point after installation the Excel file is not created and you may receive an error.
Install the Open XML SDK on all the IIS Servers hosting SmartForms. You can download the installation package from Microsoft with the following link: Open XML SDK for Microsoft Office