Some information

Operating system: Windows 10
Minecraft version: 1.14.4
Baritone version: 1.14.4

Exception, error or logs

[18:32:50] [main/INFO]: [CHAT] [Baritone] > build tower-of-five-lords.schematic
[18:32:50] [main/INFO]: [CHAT] [Baritone] Successfully loaded schematic for building
[18:32:50] [main/INFO]: [CHAT] [Baritone] Origin: BetterBlockPos{x=-93,y=4,z=-245}
[18:32:50] [main/INFO]: [CHAT] [Baritone] Unable to do it. Pausing. resume to resume, cancel to cancel
[18:32:50] [pool-6-thread-1/INFO]: [STDOUT]: Loading region -2,-2 from disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:32:50] [pool-6-thread-1/INFO]: [STDOUT]: Loaded region successfully in 58ms
[18:32:50] [pool-6-thread-1/INFO]: [STDOUT]: Loading region -2,-1 from disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:32:51] [pool-6-thread-1/INFO]: [STDOUT]: Loaded region successfully in 412ms
[18:32:51] [pool-6-thread-1/INFO]: [STDOUT]: Loading region -2,0 from disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:32:51] [pool-6-thread-1/INFO]: [STDOUT]: Loaded region successfully in 393ms
[18:32:59] [main/INFO]: [CHAT] [Baritone] > resume
[18:32:59] [main/INFO]: [CHAT] [Baritone] Not paused
[18:32:59] [main/INFO]: [CHAT] [Baritone] Unable to do it. Pausing. resume to resume, cancel to cancel
[18:33:04] [main/INFO]: [CHAT] [Baritone] > resume
[18:33:04] [main/INFO]: [CHAT] [Baritone] Not paused
[18:33:04] [main/INFO]: [CHAT] [Baritone] Unable to do it. Pausing. resume to resume, cancel to cancel
[18:33:05] [pool-6-thread-2/INFO]: [STDOUT]: Saving region -1,-1 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-3/INFO]: [STDOUT]: Saving region -1,-2 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-1/INFO]: [STDOUT]: Saving region 0,-2 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-5/INFO]: [STDOUT]: Saving region 0,0 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-6/INFO]: [STDOUT]: Saving region 0,-1 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-7/INFO]: [STDOUT]: Saving region -1,0 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-4/INFO]: [STDOUT]: Saving region -2,0 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-2/INFO]: [STDOUT]: Saving region -2,-2 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-2/INFO]: [STDOUT]: Saved region successfully
[18:33:05] [ForkJoinPool.commonPool-worker-2/INFO]: [STDOUT]: Saving region -2,-1 to disk C:\Users\bdjon\AppData\Roaming.minecraft\saves\Creative 2\baritone\DIM0\cache
[18:33:05] [ForkJoinPool.commonPool-worker-1/INFO]: [STDOUT]: Saved region successfully
[18:33:05] [ForkJoinPool.commonPool-worker-3/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [ForkJoinPool.commonPool-worker-4/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [ForkJoinPool.commonPool-worker-6/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [ForkJoinPool.commonPool-worker-5/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [ForkJoinPool.commonPool-worker-2/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [ForkJoinPool.commonPool-worker-7/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [pool-6-thread-2/INFO]: [STDOUT]: Saved region successfully
[18:33:06] [pool-6-thread-2/INFO]: [STDOUT]: World save took 885ms
[18:37:34] [Server thread/WARN]: Can't keep up! Is the server overloaded? Running 3050ms or 61 ticks behind
[18:41:03] [main/INFO]: [CHAT] [Baritone] > build tower-of-five-lords.schematic
[18:41:03] [main/INFO]: [CHAT] [Baritone] Successfully loaded schematic for building
[18:41:03] [main/INFO]: [CHAT] [Baritone] Origin: BetterBlockPos{x=-69,y=4,z=-223}
[18:41:03] [main/INFO]: [CHAT] [Baritone] Unable to do it. Pausing. resume to resume, cancel to cancel

Final checklist

• I know how to properly use check boxes
• I have included the version of Minecraft I'm running, baritone's version and forge mods (if used).
• I have included logs, exceptions and / or steps to reproduce the issue.
• I have not used any OwO's or UwU's in this issue.

I have tried searching past issues and couldn't resolve this issue.

So as it turns out, the #build command often struggles with complex structures, or structures containing fluids, but a common cause for that error is that it wants to place a block that isn't in your hotbar, or your inventory if #allowinventory is set.

On top of that, functionality to build stairs, fences and some other directional blocks are not entirely implemented.

@fw4hre0xxq is right.
It would be perfect if baritone was able to tell which block it wants. It's kind of difficult to guess.