What we need to know:
OS and version?
Beside, there is no known error with the mouse wheel handling. Works perfect on my CC 2015.1 on W7.
Please check you mouse settings (set defaults).
What exactly do you mean by "When I try to scroll inside the folders it does not work in grid"?
The cursor is either in the folder area or in the grid area. Where is the cursor when this happens.
In the Folter area. When i am down in smartselections it works. Only up in folders i have to move the slider the mouse wheel does not work.
I have the same problem
with Lightroom 6.5.1
Windows 7 Home Premium Sp1 64Bit
When I put the cursor over the scrollbar itself the mouse wheel functions, but when the cursor hovers over the folder area the mouse wheel is ignored. In the grid Area everything is ok again.
In Lightroom 4 this worked.
This is bad for me, because I have quite some folders and often scroll through them.
p.s. Once direct after opening Lightroom it even worked in the folder area, after klicking in the folder area it still worked, but after clicking in the grid area ist stopped working even after reclicking the folder area.