[Microsoft][ODBC SQL Server Driver]Invalid character value for cast specifi

Question

[Microsoft][ODBC SQL Server Driver]Invalid character value for cast specification
An you help me with this error?
This is the problemativ query:
Search QUERY : SELECT DISTINCT theK_files.fileid, theK_files.name, theK_files.t
itle, theK_files.description, theK_users1.name AS AuthorName, theK_users1.surn
ame AS AuthorSurname, [theK_file-extensions].name AS Extension, theK_files.publ
ished, theK_files.updated FROM theK_users INNER JOIN [theK_users-to-groups] ON
theK_users.userid = [theK_users-to-groups].userid INNER JOIN theK_usergroups
ON [theK_users-to-groups].groupid = theK_usergroups.groupid INNER JOIN [theK_g
roups-to-files] ON theK_usergroups.groupid = [theK_groups-to-files].groupid INN
ER JOIN theK_files ON [theK_groups-to-files].fileid = theK_files.fileid INNER
JOIN theK_users theK_users1 ON theK_files.authorid = theK_users1.userid INNER
JOIN [theK_file-extensions] ON theK_files.extensionid = [theK_file-extensions]
.extensionid WHERE theK_users.userid = '1' AND theK_files.extensionid = '1' AN
D ( theK_files.name LIKE '%a%' OR theK_users1.name LIKE '%a%' OR theK_files.de
scription LIKE '%a%' )

Answer 1

are these columns character/string/varchar:
theK_users.userid = '1'
theK_files.extensionid = '1'
if these are number columns, change them to
theK_users.userid = 1
theK_files.extensionid = 1
Jamie