Why do I get this Synthesis error?

I am building a variant of a working project, using Quartus Prime Lite.

It fails Analysis & Synthesis right at the end (97%).

I have tried in V17.1.0 and 18.1, same error with both.

It occurred after I modified an Avalon FIFO memory component in my qsys system.

When I compare the sdc file from this project with my earlier successful project, only the project names (my_proj) are different.

Any Ideas/workarounds?

Thanks John.

Info (332104): Reading SDC File: 'd:/sandbox/wh/db/ip/my_proj/submodules/my_proj_fifo_0.sdc'

Error (332000): ERROR: You must open a project before you can use this command.

while executing

"get_names -entity $search_entity -filter * -node_type hierarchy"

(procedure "altera_private_get_entity_instances::find_instances_of_entit..." line 14)

invoked from within

"altera_private_get_entity_instances::find_instances_of_entity $entity_name $nowarn"

(procedure "get_entity_instances_internal" line 72)

invoked from within

"get_entity_instances_internal 0 my_proj_fifo_0"

invoked from within

"get_entity_instances $entity_name"

(procedure "apply_sdc_pre_dcfifo" line 3)

invoked from within

"apply_sdc_pre_dcfifo my_proj_fifo_0"

(file "d:/sandbox/wh/db/ip/my_proj/submodules/my_proj_fifo_0.sdc" line 82)