"RuntimeError: can't start new thread" appears when I use the script to generate data.

Dear madgraph developer：
I try to use scripts to generate many cases with different parameters. But every time after running for a long time, an error will occur:
Command "import /home/usr/usr/madgraph/madgraph.sh" interrupted in sub-command:
"launch" with error:
RuntimeError : can't start new thread
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in 'MG5_debug'.
Please attach this file to your report.
Madgraph.sh is my script, and the content is
import model mixing
define q = u d c s b
define q~ = u~ d~ c~ s~ b~
generate mu+ mu- > q q~
output mumuToqqdifferentEtaAndMZp2
launch mumuToqqdifferentEtaAndMZp2
launch
set MZp = 1000
set WZp = 20.
set ebeam1 = 500
set ebeam2 = 500
set eta = 0.01
launch
set MZp = 1000
set WZp = 20.
set ebeam1 = 500
set ebeam2 = 500
set eta = 0.0148982
launch
set MZp = 1000
set WZp = 20.
set ebeam1 = 500
set ebeam2 = 500
set eta = 0.0197964
... ...

I don't know how to solve this problem.
                                                                                    LU