I get an 'Apex Class Invalid' error

Question

When using the 'Run an Apex Class' action, I get an error message stating 'Apex Class invalid'.

Answer

Recompiling your classes will solve this:

1. Go to Salesforce Setup > Apex Classes

2. At the Apex Classes main page, click Compile All Classes
   

To prevent this from happening again, enable compiling upon deploy:

1. Go to Salesforce Setup > **Apex Settings

   **

2. Enable Perform Synchronous Compile on Deploy

3. Click Save