You have a very big workflow that cannot be opened because you get a Java heap space error message.
Your workflow is very big (large number of nodes).
Your system has a large number of attributes.
Error messages referring to Java heap space are displayed when the workflow of a task type or a workflow task of a project are opened.
First of all, try to limit the number of nodes in the workflow. It is a general good practice to split up workflows in logical and reusable parts. This will also help you maintain and troubleshoot your workflows.
If that does not help, increase the heap size of Java applets of your browser:
Open the workflow you want to see (in a project or a task type).
Right-click the Java icon in the System tray and click Open the Java Control Panel.