I would suggest you to check and revise the amount of tags, the date/time range and the number of values you are requesting on that graph.
Any way, if this is a use problem then, in the nicest way possible, I would like to invite you to contact our Technical Support team instead (TechSupport@osisoft.com - +1-510-297-5828). The OSIsoft vCampus program and its various features (such as this particular "SharePoint Development & Integration" discussion forum) are really meant for programming, development and integration topics. Just like Microsoft's MSDN. On the other hand, "end-usero" and "PI administration" questions (e.g. installation, configuration, usage, etc.) are still best handled by our technical support team.
If you feel this is a missunderstanding feel free to reply to this thread.