AttributeError: 'SymbolSTRSLICE' object has... (*solved*)

[programandala.net]

For the second time, I get the following output (version 1.2.5):

marcos$ zxb.py --tap --autorun --BASIC --sinclair colegio_erevest_4.bas
Generating LALR tables
Generating LALR tables
WARNING: Token 'UMINUS' defined, but not used
WARNING: There is 1 unused token
Traceback (most recent call last):
File "/home/marcos/bin/zxb.py", line 255, in <module>
sys.exit(main(sys.argv)) # Exit
File "/home/marcos/bin/zxb.py", line 203, in main
zxbtrad.traverse(zxbtrad.FUNCTIONS) # This will fill MEMORY with pending functions
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 250, in traverse
traverse(l)
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 959, in traverse
traverse(i)
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 257, in traverse
traverse(i)
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 770, in traverse
traverse(tree.next[1])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 720, in traverse
traverse(tree.next[0])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 1004, in traverse
traverse(tree.next[i])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 1008, in traverse
traverse(tree.next[0])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 569, in traverse
traverse(tree.next[0])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 375, in traverse
traverse(tree.next[0])
File "/opt/zxbasic/1.2.5/zxbtrad.py", line 530, in traverse
if tree.next[0].token != 'STRING' and tree.next[0].token != 'ID' and tree.next[0].symbol._mangled[0] != '_':
AttributeError: 'SymbolSTRSLICE' object has no attribute '_mangled'

I've searched for "mangled" in the forums, but there's no message about it.

It seems it happens when no more syntax errors are found in the source, but I'm not sure. Any clue? Is it a compiler issue or is it caused by my program?