I haven't seen an error quite like this before. The 'Conversion' part of the error message is being generated by your JDBC driver or SQL server, it doesn't come directly from PWM.
To diagnose this your going to need to examine the PWM server logs, probably at TRACE level. It may also be helpful to enable the JDBC trace at 'Settings ⇨ Database (Remote) ⇨ Advanced ⇨ Database Trace Logging'. This shows the SQL commands being generated.