I ran smilint on the ZyXEL MIB which produces quite a few errors - but also a ton of these:
ZYXEL-MIB.txt:74: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:77: {internal-other} syntax error, unexpected ACCESS ZYXEL-MIB.txt:85: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:89: {internal-other} syntax error, unexpected ACCESS ZYXEL-MIB.txt:97: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:101: {internal-other} syntax error, unexpected ACCESS ZYXEL-MIB.txt:109: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:112: {internal-other} syntax error, unexpected ACCESS ZYXEL-MIB.txt:122: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:133: {internal-other} syntax error, unexpected ACCESS ZYXEL-MIB.txt:141: {internal-other} syntax error, unexpected UPPERCASE_IDENTIFIER, expecting LOWERCASE_IDENTIFIER ZYXEL-MIB.txt:144: {internal-other} syntax error, unexpected ACCESS
The explanation of 'internal-other' asked that I submit a report.
An unmodified version of what appears to be the most recent ZyXEL MIB is available here: http://jessen.ch/files/Zyxel.mib