Please help me with this database error (1064) message

[JDD]

Hello,

does anybody know how this error could occur...

For most of our users the Board seems to be working pretty well. But I get these database errors to my mail account:

Database error in vBulletin: Invalid SQL: SELECT COUNT(*) AS messages FROM privatemessage WHERE userid=122 AND fromuserid<> AND fromuserid<>442 mysql error: You have an error in your SQL syntax near 'AND fromuserid<>442' at line 1 mysql error number: 1064

or

Database error in vBulletin: Invalid SQL: SELECT COUNT(*) AS messages FROM privatemessage WHERE userid=253 AND fromuserid<> AND fromuserid<>92 AND fromuserid<>484 mysql error: You have an error in your SQL syntax near 'AND fromuserid<>92 AND fromuserid<>484' at line 1 mysql error number: 1064

there are other messages but always Error 1064 with different userids

any help would be appreciated

thx

JDD