As you say, the question pronoun corresponding to

> Ich komme nicht auf das Netzwerklaufwerk

is ***wohin***, so it's rather a determination of the **direction** than of location. This makes the difference because the prepositions

> an, auf, hinter, in, neben, über, unter, vor, zwischen

are called [***Wechselpräposition***](https://learngerman.dw.com/de/wechselpr%C3%A4positionen-3/l-40581904/gr-40585492). Whether they govern (~ require; trigger) the dative or the accusative depends on whether they describe a location (dative) or a direction (accusative).