Other mistake: As Picard and Robert walk alongside the large bush just before their scuffle, two outgrowth branches on the bush get snagged onto the camera and can be seen snapping back into place.
Other mistake: The ship warp core was damaged by an explosion earlier and was offline in the first 32 minutes of the episode. But the ship's CGI indicates that it was online all through the episode.
Other mistake: As the camera looks at the Enterprise as a transitional view, part of the decal for the registry number is visible.
Remember Me - S4-E5
Other mistake: Toward the end, Beverly gets in the turbo lift to go to Engineering. As it starts, you see the lights to her left strobe top down. This is to indicate movement. However, since the lift was at the bridge level, the lights should have gone from bottom up, showing that the lift is going down.
Nth Degree - S4-E19
Other mistake: After Data reports the bypass blocked, Riker goes to call to Barclay. The chirp preceding the computer, now Barclay's, response occurs almost simultaneously with the call, rather than a second or two gap between the call and chirp.
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.