Data aggregation error

[mlofgrenvt]

"Couldn't store in SignalId Column. Expected type is Int32. ---> System.FormatException: Input string was not in a correct format."

The database table SignalEventCountAggregations uses nvarchar for SignalId, but this code is looking for Int?. Our SignalIds have letters in them. Am I doing something wrong?
Full error below

Saving Signal Event Data to Database...

Unhandled Exception: System.AggregateException: One or more errors occurred. ---> System.ArgumentException: Input string was not in a correct format.Couldn't store in SignalId Column. Expected type is Int32. ---> System.FormatException: Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
at System.String.System.IConvertible.ToInt32(IFormatProvider provider)
at System.Data.Common.Int32Storage.Set(Int32 record, Object value)
at System.Data.DataColumn.set_Item(Int32 record, Object value)
--- End of inner exception stack trace ---
at System.Data.DataColumn.set_Item(Int32 record, Object value)
at System.Data.DataRow.set_Item(DataColumn column, Object value)
at System.Data.DataRow.set_Item(String columnName, Object value)
at MOE.Common.Business.DataAggregation.DataAggregation.BulkSavePhaseTerminationData() in C:\Projects\GitHub\ATSPM\MOE.Common\Business\DataAggregation\DataAggregation.cs:line 613
at MOE.Common.Business.DataAggregation.DataAggregation.b__15_9() in C:\Projects\GitHub\ATSPM\MOE.Common\Business\DataAggregation\DataAggregation.cs:line 186
at System.Threading.Tasks.Parallel.<>c__DisplayClass4_0.b__0()
--- End of inner exception stack trace ---
at System.Threading.Tasks.Parallel.Invoke(ParallelOptions parallelOptions, Action[] actions)
at System.Threading.Tasks.Parallel.Invoke(Action[] actions)
at MOE.Common.Business.DataAggregation.DataAggregation.BulkSaveAllAggregateDataInParallel() in C:\Projects\GitHub\ATSPM\MOE.Common\Business\DataAggregation\DataAggregation.cs:line 100
at MOE.Common.Business.DataAggregation.DataAggregation.StartAggregation(String[] args) in C:\Projects\GitHub\ATSPM\MOE.Common\Business\DataAggregation\DataAggregation.cs:line 93
at AggregateATSPMData.AggregateAtspmData.Main(String[] args) in C:\Projects\GitHub\ATSPM\ArchiveMetricData\AggregateAtspmData.cs:line 26