help for Cadence® Encounter command buildtiminggraph

When I first import the lef/lib/.v/.sdc files to the encounter ,then
I use
amoebaplace to do a prototyping place ,then I use the buildtimingraph
,but there are being error in the terminal telling me that it can not
generating timing graph.
*** Initialize timing graph (0 nodes, 0 edges) (cpu=0:00:00.0
mem=185.5M)**
**WARN: Empty timing graph!!!
why only 0 nodes, 0 edges? pls give me some advices,thanks!



more detail as following:
<CMD> amoebaPlace -fp
<CMD> buildtiminggraph

*** Starting xroute (mem=182.4M) ***

options: glbDetour reduceNode obstruct2 obstruct4 spreadOut
multiOuterRow moveTermZ fixAirConnect spacingTable pinAndObsSpacing
multiVoidRow wideBlockageSpacing MSLayer
Number of redundant fterm=75
routingBox: (520 560) (5018520 4977840)
coreBox: (509520 498400) (4510440 4490080)
nrIoRowLo/Hi = 41/40 nrIoColLo/Hi = 34/34
Init all gpins ...
Number of multi-gpin terms=0, multi-gpins=0, moved blk term=19/19
Number of initial reassigned term = 0

Phase 1a route (0:00:00.4 183.0M):
Est net length = 8.763e+05um = 4.061e+05H + 4.702e+05V
Suboptimal net = 442 out of 3721 (11.9% nets) (10.2% len over box)
Usage: (3.5%H 3.6%V) = (4.224e+05um 5.283e+05um) = (127225 104696)
Obstruct: 91724 = 45862 (14.3%H) + 45862 (14.3%V)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 120 = 120 (0.04% H) + 0 (0.00% V)

Phase 1b route (0:00:00.7 183.0M):
Usage: (3.5%H 3.6%V) = (4.217e+05um 5.277e+05um) = (127036 104585)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 2 = 2 (0.00% H) + 0 (0.00% V)

Phase 1c route (0:00:00.4 183.0M):
Usage: (3.5%H 3.6%V) = (4.211e+05um 5.278e+05um) = (126853 104597)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 2 = 2 (0.00% H) + 0 (0.00% V)

Phase 1d route (0:00:00.8 183.0M):
Usage: (3.5%H 3.6%V) = (4.214e+05um 5.284e+05um) = (126947 104711)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 0 = 0 (0.00% H) + 0 (0.00% V)

Phase 1e route (0:00:00.6 183.0M):
Usage: (3.5%H 3.6%V) = (4.214e+05um 5.284e+05um) = (126947 104711)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 0 = 0 (0.00% H) + 0 (0.00% V)

Usage: (3.5%H 3.6%V) = (4.214e+05um 5.284e+05um) = (126947 104711)
OvInObst: 0 = 0/45862 (0.00% H) + 0/45862 (0.00% V)
Overflow: 0 = 0 (0.00% H) + 0 (0.00% V)

Congestion distribution:

Remain cntH cntV
--------------------------------------
--------------------------------------
0: 5 0.00% 2 0.00%
1: 91 0.03% 868 0.31%
2: 211 0.08% 11094 4.02%
3: 463 0.17% 68361 24.80%
4: 1217 0.44% 11220 4.07%
5: 2563 0.93% 928 0.34%
6: 4725 1.71% 469 0.17%
7: 80788 29.31% 1496 0.54%
8: 11685 4.24% 6167 2.24%
9: 2271 0.82% 4503 1.63%
10: 2025 0.73% 4617 1.68%
11: 2579 0.94% 7905 2.87%
12: 4113 1.49% 20761 7.53%
13: 5824 2.11% 95769 34.74%
14: 7882 2.86% 28598 10.38%
15: 19914 7.22% 52 0.02%
16: 97289 35.30% 356 0.13%
17: 10318 3.74% 2 0.00%
18: 288 0.10% 2 0.00%
19: 11571 4.20% 1 0.00%
20: 9814 3.56% 12465 4.52%

Nr short=6864 85%, med=88 1% medR=1145 long=0, huge=0
Phase 1l route (0:00:02.9 185.5M):
Number of deextended terms = 19
Cleanup 120 multi-gpin terms
Prep phase2 (0:00:00.1 185.5M):


Total length: 8.760e+05um, number of vias: 30507
M1(H) length: 0.000e+00um, number of vias: 12017
M2(V) length: 1.301e+05um, number of vias: 12141
M3(H) length: 2.607e+05um, number of vias: 2661
M4(V) length: 7.292e+04um, number of vias: 2174
M5(H) length: 1.451e+05um, number of vias: 1514
M6(V) length: 2.671e+05um
*** Completed Phase 1 route (0:00:07.9 185.5M) ***

Phase 2a route (0:00:01.5 185.5M)
Phase 2b route (0:00:01.6 185.5M)

Total length: 8.906e+05um, number of vias: 30628
M1(H) length: 3.964e+03um, number of vias: 12065
M2(V) length: 1.398e+05um, number of vias: 12168
M3(H) length: 2.614e+05um, number of vias: 2685
M4(V) length: 7.477e+04um, number of vias: 2196
M5(H) length: 1.451e+05um, number of vias: 1514
M6(V) length: 2.656e+05um
*** Completed Phase 2 route (0:00:03.4 185.5M) ***

*** xroute (cpu=0:00:11.3 mem=185.5M) ***
RC Extraction for instance top
Initializing the RC extractor ...
RC Extraction Completed (CPU Time= 0:00:00.1 MEM= 185.5M)
*** Mark 1406 set_logic ignored terminals ***
*** Read timing constraint file (0:00:00.0) ***
*** Constant propagation (cpu=0:00:00.0 mem=185.5M) ***
*** Mark 13070 ignored terminals (0:00:00.1) ***
*** Initialize timing graph (0 nodes, 0 edges) (cpu=0:00:00.0
mem=185.5M) ***
**WARN: Empty timing graph!!!

*** Memory Usage v0.58 (Current mem = 185.488M, initial mem = 106.113M)
***
--- Ending "First Encounter" (totcpu=0:03:38, real=0:29:17, mem=185.5M)
---