New to Houdini and got the Free version (Apprentice 18.5.633) and had the same issue.
Searched online and found it's because manta renderer uses TEMP files which are located in your users %temp% folder in the C drive (C:\Users\firstname lastname\AppData\Local\Temp\houdini_temp).
Since my pc's user account is my full name (firstname lastname) this filepath contains a space,
which causes manta renderer to freak out.
A simple, easy fix is to add this text to a new line at the bottom of your houdini.env file located in your C drives documents folder (C:\Users\firstname lastname\Documents\houdini18.5)
HOUDINI_TEMP_DIR = (insert path of new location here without the brackets. make sure the path has no spaces in it!)
e.g.
HOUDINI_TEMP_DIR = D:\Users\User2\AppData\Local\Temp\houdini_temp
Since I'm on a laptop with a SSD and HDD, I simply mimiced the directory onto my other drive. That's just how I set things up. Yours can be anywhere as long as the file path does not have spaces.
Restart Houdini and the problem should be solved.
Solution found from Right-Brained Tutorials on Youtube:
https://www.youtube.com/watch?v=GHvtpOFEqFs [
www.youtube.com]
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Additionally, if you get this error message
Unable to load HFS OpenCL platform.
just add this line to the same file:
HOUDINI_USE_HFS_OCL=0
I got this solution from u/Spicy_Rendang on the reddit thread:
https://www.reddit.com/r/Houdini/comments/l2o4io/unable_to_load_hfs_opencl_platform/ [
www.reddit.com]