SharePoint An unexpected error: Not firing button_Click function and goes to Web parts maintenance page

enter image description hereI have dropped a webpart on publishing page but when i click on (process)button it transfer me to this error:

Sorry, something went wrong An unexpected error has occurred. Web Parts Maintenance Page: If you have permission, you can use this page to temporarily close Web Parts or remove personal settings. For more information, contact your site administrator.

My webpart contains a search button and a process button and a gridview, functionality of process button is to read an excel file and display it in a gridview the whole process is working fine on other site but is not working on my QA site where testing is going on and because of this I can not debuggingSnapshot

scenario is I have to select file and process.

can anybody helps me out why it is transferring me to the “Web Parts Maintenance Page

the same thing is working fine on the other site