You get the message that your gantt is not properly configured
Your gantt is properly configured if:
All of the 4 mandatory columns have been mapped in the "Map Your Sheet" page (those with a " * " are mandatory). The mandatory columns are
At least one of the rows in the selected sheet is a valid task. A row in the selected sheet constitutes a "valid" task if it has a valid value in each of the 4 mandatory columns. In same cases you can have rows in your gantt that are not tasks (e.g. a row with a sum of the days or a row that divides one phase from another) or you can have other rows under your tasks with other information (e.g. comments or charts). These rows are automatically ignored by SlickGantt if the information in the 4 mandatory columns don't contain a valid value.
The Gantt would not load (the loading logo doesn't disappear) or the Configuration page is stuck in "Loading..."
This error is typically caused by being logged in with multiple Google accounts within the same browser page. Unfortunately Google App Scripts has a known issue that prevents to correctly deal with situations like this: basically having multiple accounts active in the browser "confuses" the app script who tries to use the wrong user to perform the action, firing several kind of Authorization issues.
You might be wondering why not all the Add-on you are using might be affected by that: only the Add-ons using a custom UI that interacts with the script back-end are affected (when the user interface is calling the back-end to perform an action).
If you have time (and good sense of humor) and want to see the bug opened with the Google team you can find it here.
HOW TO SOLVE THE ISSUE
You have 3 options:
1) Log out from all the other Google accounts in your browser. You can do it clicking on your picture on the top-right corner of the page when you are in your spreadsheet
2) Use Chrome profiles: this is a best practice working with multiple accounts and provides a good segmentation between accounts. Quoting Google, using different profiles is suggested for "keeping your different accounts, like work and personal, separate ".
Using different profiles also allows you to:
Have your bookmarks and Favorites segmented
Reopen a user session with all the windows that were opened for that account
Have different navigation histories
Here all the info you need to create different profiles.
3) Use an Incognito Window
Your gantt is grey (does not have colors)
The colors are assigned to each task that is marked as "Main task". If the gantt is grey it means that your tasks do not have any "type" assigned. Do the following:
Go to "Map your Sheet" option in the Slick Gantt menu
Double check that the right sheet is selected (in my example the name is "SlickGantt example 879")
On the line "Task Type" click on the orange button "Prepare": this will create a column in your sheet ready to accommodate the information about the task type
Go back to your sheet and you'll see a new column "Task Type" with a drop down list available: select "Main task" for your main tasks. Each main task (and related sub tasks) will have the same color.
If you want to change the colors assigned to tasks, use the option "Colors" in the menu.
Your Resources are duplicated
SlickGantt will create a resource profile for each name stored in each cell under the column that stores the resources.
If you have more than one resource, you can use the comma " , " to separate the resources. Note that you should not add any space after the comma, otherwise the resource might be duplicated.
Row 1: Bob
Row 2: John,Bob
Row 3: Jim,Clark
This will create the following resources: Bob, John, Jim, Clark
Row 1: Bob
Row 2: John, Bob (-> space after the comma)
Row 3: Jim,Clark
This will create the following resources: Bob, Bob(with an initial space), John, Jim, Clark
If you have a duplicate resource or if you want to delete a resource that you are not using anymore you can go to the page "Resources" and use the "X" button to delete resources that are not currently in use.
Issue using Explorer or Firefox
SlickGantt is supported only on Chrome at the moment