I also got same problem while fetchibg data from a entity having huge data ..then i added some filters to it and set the max records to 1000 and it starts working fine.
Also i have got the same issue while running a exe from my code and waiting to finish it ..some time it took long and i got the request timeout issue.

Thats true ...but the screen was dead slow and i maximum time i was getting request timeout. I put few filters there to narrow down there search and anyways they are just seeing 50 records per page .

Hi Eric,

It depends on how many records you want to display on page. If you are displaying entire query result on page and if query returns more than 300 records, sometimes inside the browser it will give Javascript related errors and that's why you must be getting this issue "There was an error processing your request. Please try again later...".
So it would be better to limit no of records to be displayed per page. As Pramod said, you can divide 50 records per page. If your data is large, you can limit it to 100 records per page and use list_navigation control to traverse through all the records.

Thanks,
Suraj Borade