There Is a Number of vs. There Are a Number of

In general, the choice between there is vs. there are depends on the noun that follows the phrase. However, when it comes to the phrases there is a number and there are a number, the choice depends on the emphasis that you want to make.

Use there is a number if you want to emphasize a group as a whole. Use there are a number if you want to emphasize individual members in a group.

Example 1

When you test a plan, there are a number of issues that may occur in the Orchestrator UI: [issues are listed explicitly]

• Orchestrator calculates the completion percentage wrong and displays the execution progress bar incorrectly.
• Lab group states are shown incorrectly.
• Plan states are shown incorrectly.

Example 2

There is a number of ways to update VMware Tools. For example, you can do it manually or configure VMs to perform automatic updates the next time they reboot. [options are not that important themselves]