Continuity mistake: In the beginning of the episode, Riker, Geordi, Worf, Data, and Pulaski are playing poker. Pulaski puts two neat stacks of chips in the center beside some chips in a pile. It then shows Worf putting similar stacks in the center but Pulaski's stacks are not visible and they should be. Then when Worf wins the hand, the camera is showing a wide shot of him pulling the chips towards him and you can see his and Pulaski's neat stacks of chips.
Continuity mistake: When Data is dealing the cards for 7-card stud, they show him dealing 1 card to everyone. In the close up, he's now dealing everyone a 2nd card. When it cuts to his hands however, everyone only has 1 card and he's dealing them a 2nd card again.
Visible crew/equipment: As La Forge and Crusher leave the bridge, and the camera closes in on Riker, there's a shadow of a piece of filming equipment on the wall behind and to the left of his head, at the upper right of the shot.
Visible crew/equipment: As Picard goes to sit in his seat, there's a shadow of the boom mike playing across the wall above Burke and Kolrami's heads.
Revealing mistake: When looking at Kolrami, the line between his make up and actual skin tone can be seen between his scalp, hairline, and the back of his neck.
Visible crew/equipment: As Kolrami talks to Picard from beside the aquarium, you can see the studio light panels reflected on the glass.
Continuity mistake: Near the end, when Pulaski finally stops the infection in Riker and is just about to contact Picard with her success, look at Riker lying on the table. His eyes are open, then he closes them slowly. The next scene has Riker opening his eyes for the first time after recovering from the procedure.
Other mistake: In this episode, in Riker's memory, the encounter between him and Quinn is re-lived. As Quinn starts to attack Riker, you can see Riker's stunt double's face, and tell that it's Quinn's stunt double, as the hair is smooth, not styled. Also, Riker is a few inches taller than Quinn, but in the onset of the attack, they're equal heights.
Continuity mistake: After Pulaski examines Riker's leg, and readies to beam up, he leans to the right to get up. In the wide shot, he does it again.
Answer: Yes. The doors to the holodecks can be locked when in use by anyone aboard the Enterprise so they couldn't be disturbed. However, high ranking officers like Captain Picard could override the doors as it's seen that overrides are in use even for the crews quarters. Even Barclay, when he's indulging in one of his fantasies could have the doors to the holodeck unlocked by an override code.