When a material is used with Enlighten lightmaps, the number of texture samples allowed in the material is reduced. This can cause an error when compiling the shaders for a material with many texture samples.

When a material has Used With Enlighten Lightmaps selected in Details > Usage:

the number of available texture samplers is reduced
if the target shader profile supports shared samplers, only one sampler is reserved
if the target shader profile doesn't support shared samplers, the number of reserved samplers increases with the Lightmap Display Quality chosen in Project Settings > Enlighten

(Mobile) Lightmap Display Quality	SM5	SM4	METAL_MRT	METAL_SM4	ES2	METAL
High	1	1	1	1	3	4
Medium	1	1	1	1	2	3
Low	1	1	1	1	1	2

If you know the material is never used with a mesh that's lit using lightmaps, disable Used With Enlighten Lightmaps to increase the number of available texture samplers.