If you use the one-click install (and from what I can tell, about any dotproject install), you will get an error message when trying to display a gantt chart indicating that memory isn't configured properly.
The full message is:
The good news is that the fix is easy.
In the system administration panel, set the "Gantt Memory Limit" to at least 32M. Note that higher values may be necessary if many tasks are in use, but remember that DH has a fairly low limit that might cause errors if you push it too high.
The post in the dotProject forums is HERE.
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