Internal Server Error generated from Opmanager API

Attempting to add a notification profile to a device. Utilizing API for device creation and adding notes to a device works with no problem. Here's my URL in my attempt to add a notification profile:

" http://ValidServer/api/xml/discovery/addDeviceToNProfile?apiKey=ValidKey&deviceName=TestedDevice&profileName=ValidProfile&criteria=3000000000000000000000000&

performanceMonitors=DiskUtilization,Win-CPUUtilization,Win-MemoryUtilization"

The fields for server, API key, device name are exactly the same ones I use elsewhere in my script, and they work fine. The profile name is a valid, existing notification profile. When I attempt to HTTP POST my url, I receive "Internal Server Error while processing this request" error.

Please help.