Cannot select a resource for a resource request or for a task assignment in the project worksheet

Check that the desired resource is in your preferred resources list, and if not, add them. The resources that are available for selection in a resource request come from your preferred resources list. 

Regarding the project worksheet, if resource requests are enabled at the project level, then only the following resources are available:

• resources that have been added to the project team through a resource request
• resources that are exempt from resource requests