2. Having no place to park
Having their parking space abrogated for repairs is one thing. Something else entirely is another tenant or the tenant's guest using the good tenant's parking space. In many apartment complexes parking is assigned by seniority. Good spots are prized possessions, earned by longevity in a complex. To come home and find some bozo's car in his space will start a good tenant's blood boiling, and for good reason.
Parking issues rank right up there with noise for things that most irritate tenants. Ask any police officer who does community meetings, and he or she will tell you that even though the police officer has come to talk about crime prevention, the questions will always devolve to traffic problems: misuse of the streets.
By the same token, get tenants talking about what bugs them most, and somebody else's car in their parking space will go right to the top of the list.
You have probably created specific rules about parking for your rental properties, assuming that you have to deal with it at all. Single-family homes don't have a problem, since there are no other tenants to steal a parking spot. But in any rental property that has an actual parking lot, count on there being disagreements over parking spaces, even if you have hard and fast rules.
Just as with rules about disturbing neighbors, enforce the parking rules to the letter. That means warning letters and notices to tenants who break the rules and calling the tow truck. There is no excuse, period, for parking in another tenant's parking spot, except if the other tenant has given permission.