serial vs parallel for ar

[PATTON, BILLY \(SBCSI\)]

I'm trying to add files to a .a file.  As long as I don't run make with
-j it runs ok. But when I run with the -j I get the following error
messages:
ar:
/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/lib/libinfgn
.a not in archive format
make: ***
[/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/gipasswd.o]
Error 1
make: *** Waiting for unfinished jobs....
ar:
/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/lib/libinfgn
.a not in archive format
make: ***
[/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/cryptut.o]
Error 1
ar:
/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/lib/libinfgn
.a not in archive format
make: ***
[/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/giconv.o]
Error 1
ar:
/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/lib/libinfgn
.a not in archive format
make: ***
[/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/extfsh.o]
Error 1
ar:
/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/lib/libinfgn
.a not in archive format
make: ***
[/makefile_test/dev/bp1497/test/v0608/PRODUCT_TREE/ldb/infgn/gifile.o]
Error 1

It is probably the fact that several processes are trying to access this
.a at the same time.
What can I do?