If you could post the code you're using for the jump action, that would help us get to the root of the issue faster. The problem you described above will occur if you have moving objects marked "solid". Solid is alright for some cases of inanimate objects- I have used it before for floors- but I would not recommend it for characters. Here is a possible fix to your problem.
In your floor object- check the solid box. Create a collision event in the floor object for when the player object collides with the floor, and add this script.
Code:
move_contact_solid(direction,12)
vspeed = 0;
Then, go into your player object. Make sure "solid" is unchecked. Add this code into the key or mouse press event that makes your character jump.
Code:
if!(place_empty(x,y+1))
{
hspeed = 0;
}
Also in the player object, a step event. Add this script to the event. For the program I'm writing, I have the jump event triggered by pressing the space bar. If you want it to be triggered by a different event, simply remove the "vk_space" and replace it with your desired key.
Code:
if(keyboard_check_pressed(vk_space))
{
vspeed -= 10;
}
//gravity
if(place_empty(x,y+1))
{
gravity = 0.5
}
else
{
gravity = 0
}
Let me know if that helps.